Welcome

The non-profit, Friends of Mineralogy (FM), a national organization founded in 1970, includes nearly a dozen chapters from coast to coast, whose members share a common love of minerals. FM’s objective is to promote, support, protect, and expand the collecting of mineral specimens, while furthering the recognition of the scientific, economic, and aesthetic value of minerals and mineral collecting. Membership includes collectors, museum curators, mineralogists, and earth science educators.  The organization is affiliated with Mindat.org, the Mineralogical Society of America (MSA), and the Mineralogical Association of Canada (MAC).

Among its many activities, FM regional chapters sponsor symposiums, and collecting trips to quarries, mine dumps, and mines across the country.  FM has made its voice heard whenever proposals are made to close mineral museums or collecting sites.  National FM co-sponsors symposiums held annually at the Tucson Gem & Mineral Show, and contributes support and speakers to other mineral symposiums.  FM presents annual awards for best article published in each of the following publications: The Mineralogical RecordRocks & MineralsMineral News, and Mineral Monographs.  It also gives awards to the best institutional and individual educational exhibit cases displayed at the Denver and Tucson gem and mineral shows.


Please send tax-deductible donations to support Friends of Mineralogy, a non-profit 501(c)3 organization, in care of Bruce W. Bridenbecker, Treasurer, 7528 Lucerne Vista Ave, Yucca Valley, CA 92284, made out to Friends of Mineralogy.

INSTAGRAM

  • by friendsofmineralogy 3 days ago
    Know what you are lighting up this weekend? All the beautiful bright flaming colors of fireworks are derived from minerals. When fireworks explode, the heat from the explosion causes metal salts to absorb energy from the heat and to emit light of different colors. The color of the light depends on the type of metal or combination of metals present, because the electrons within different metals will excite to different energy states that emit light of a specific energy and that will produce a characteristic color. The heated elements of strontium (usually obtained from celestine, strontium sulfate) produce red light. The addition of sodium salts (from sodium nitrate or sodium chloride) will produce a yellow to orange light. Copper compounds, while producing blue light on their own, will produce lovely purples when mixed with the red of strontium. Green light is from barium (derived from barite, barium sulfate) combined with chlorine. Flashes and bangs and sparks come from aluminum powder or iron filings. Many consumer fireworks are made in China, but the raw materials in American-made fireworks may also come from all over the world. The USA produces quite a bit of copper, but imports most of its strontium from Mexico, barite from China, and sodium nitrate from South America. To assemble a firework, the metals salts and any flashing or spark material are carefully packed, alongside with gunpowder, into an aerial shell in small globs called “stars”. The shell is on a delay fuse, timed carefully to ignite after it is shot into the air from lifting charge. It is the stars exploding that we see as the dazzling bursts of light. These beautiful explosions can reach temperatures of up to 1,800 °F (1,000 °C), as hot as lava! Please remember that much of the American west is still facing significant drought conditions, and to always respect safety of friends and neighbors - please use caution this holiday! : Graphic by Erin Delventhal
  • by friendsofmineralogy 6 days ago
    These golden needles are not hair or straw – they are individual rutile (titanium dioxide) crystals, the longest of which are around one centimeter long. Rutile is more commonly found as more ‘chunky’ darkly opaque to reddish striated prisms; hence why it was named from the Latin rutilus, meaning "red." Rutile is one of the minerals that frequently grows oriented along the crystal faces of other minerals. In this example, the fine rutile needles are oriented along the axes of hematite crystals visible near the bottom of the photograph. This phenomenon, called “epitaxy,” can result in stunningly beautiful starbursts of golden rutile crystals with centers of metallic hematite, embedded within a quartz crystal. Oriented micro growths of rutile crystals are often the cause of ‘star sapphires’ and similar gems. Sands with high concentrations of rutile and other metal ore minerals are known as ‘heavy mineral sands.’ These sands are the result of weathering of igneous and metamorphic rocks with these constituents. Waves and winds have helped to sort the heavy metallic sand grains into higher concentration deposits that can be profitably mined. Rutile sand is then used to manufacture white pigments and refractory ceramics and to produce titanium metal. Rutile is the most common form of several natural titanium dioxides. Others include anatase and brookite…we’ll get there. : Rob Lavinsky & irocks.com.  @arkenstone_minerals  Novo Horizonte, Bahia, Brazil ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the oxides!  #oxides   #rutile   #minerals   #mineralcollecting   #crystals   #geologyrocks   #mineralogy   #science   #chemistry   #earthscience   #mineralcollector   #rocksandminerals   #geologygeek   #earthtreasures 
  • by friendsofmineralogy 1 week ago
    Faden quartz is one of the most unique and distinctive growth forms of quartz, often (but not always) taking the form of flattened prisms linked along a central, wispy line. That wispy line can look like a white thread or string: “faden” (pronounced “fah-den”) is the German word for string. The “faden” is clearly visible in the flattened prism in our example, which is an unusual example of faden quartz because it is still attached to the host rock matrix. Why is it unusual to find Faden quartz crystals still attached to matrix? Because faden quartz forms in rock fissures that widen slowly and steadily. When the fissure opens, small quartz crystals will break on the rupture. Quartz crystal growth is faster along fractured surfaces than regular faces; so in the presence of silica-rich solution the small ruptured crystals will “heal” quickly into new crystal faces. The new crystal will bridge the fissure in the rock. As the fissure widens into a cleft, the crystal continues to grow. Where the initial growth of the faden might be thin, it becomes wider with continued growth and often assumes a platy shape. Repeated slow but continuous rupture and healing leaves a sort of scar inside the crystal in the form of the faden line. The thin line indicates that the widening of the cleft was a mostly continuous movement–if the cleft moved suddenly, the crystals would resume normal growth or develop defined cracks. The faden crystal’s original connection to the rock walls are usually quite delicate and are broken by the time humans find them, and are very difficult to extract if that connection does remain. : Jessica Robertson. Specimen from Tole, Wana, South Waziristan District, Khyber Province, Pakistan.  #quartz   #crystallography   #quartzcrystal   #geologyrocks   #mineralsofig   #earthscience   #mineralcollector   #minerals   #mineralspecimen   #crystaladdict   #crystalsofinstagram   #rocksandminerals   #geologygeek   #earthtreasures   #cabinetofcuriosities 
  • by friendsofmineralogy 2 weeks ago
    Zincite is the mineral of zinc oxide (ZnO) – the same compound that is the active ingredient in many popular “mineral” sunscreens! Zinc oxide crystals can be grown artificially in a laboratory and as a byproduct of the smelting process, but actual natural crystals of zincite are rare in nature and found in only a few places, like the Franklin Mine in New Jersey, which is also famous for a wide variety of fluorescent minerals. Large and colorful crystals of zincite can sometimes be found on the collector market, often with a story about how they formed in the smokestack of a Polish smelter or refinery that was in need of repair. While it appears that there was an incident in the 1970s where this was true, the majority of zincite crystals currently on the market are intentionally man-made. Natural and synthetic zincite is an important and useful material. Before vacuum tubes were invented, they were used as semiconductor crystal detectors in early crystal radios. As the common white powder of zinc oxide, it was used as paint and ointment at least as far back as the first century BCE. Today it is still used for these purposes, as well as in the rubber and ceramic industries, fire retardants, batteries, as a semiconductor, and much more. Pure zinc oxide is also a common food additive generally recognized as safe by the FDA -- it is the source of zinc in fortified breakfast cereals. : Rob Lavinsky & irocks.com.  @arkenstone_minerals  Crystal to 1.4 cm. Franklin Mine, Franklin Mining District, Sussex County, New Jersey, USA ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the oxides!  #oxides   #zincite   #minerals   #mineralcollecting   #crystals   #geologyrocks   #mineralogy   #science   #chemistry   #earthscience   #mineralcollector   #rocksandminerals   #geologygeek   #earthtreasures 
  • by friendsofmineralogy 3 weeks ago
    Cuprite is copper(I) oxide (Cu2O) and a minor copper ore. It can form charming cubic and octahedral forms and in red to dark colors ranging from opaque shades to a deep gemmy red. Sometimes called “ruby copper” for the color, it is rarely cut into gemstones because of its softness, 3.5-4 on the Mohs scale. Cuprite is often formed as an oxidation product of copper sulfide minerals, in the upper zones of copper deposit veins. You’ll find it in association with other copper minerals like malachite and chalcocite. The gemmiest red cuprites can be sensitive to light, and can darken into a patina color that could resemble our example (still lovely!). This light-induced decomposition is a transition of the pure cuprite surface into native copper and tenorite. If you are lucky enough to own a gemmy red cuprite crystal, some light protection is advised – storage in a drawer or box for the long term, and low light conditions when on display. : Fabre Minerals  @fabreminerals  4.2 cm. Poteryaevskoe Mine, Rubtsovsky District, Altai Krai Russia ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the oxides!  #oxides   #cuprite   #minerals   #mineralcollecting   #crystals   #geologyrocks   #mineralogy   #science   #chemistry   #earthscience   #mineralcollector   #rocksandminerals   #geologygeek   #earthtreasures 
  • by friendsofmineralogy 3 weeks ago
    Do you see a face in this agate? If so, that's pareidolia! Pareidolia is the human tendency to see recognizable patterns where none was intended in inanimate objects-- it's the reason we see animals in clouds, the Man in the Moon, and religious icons in toast or pancakes. "Smiley face" agates are a simple joy caused by our brains' keen ability to translate the banded chalcedony color patterns into facial patterns, and to project emotion into the perceived expression. University of Sydney researcher David Alais told The Gaurdian in July 2021 that “What we found was that actually these pareidolia images are processed by the same mechanism that would normally process emotion in a real face. You are somehow unable to totally turn off that face response and emotion response and see it as an object. It remains simultaneously an object and a face.”  #pareidolia   #science   #agate   #chalcedony   #smile   #minerals   #rocksandminerals   #geologyrocks   #rockhound   #simplejoys 
  • by friendsofmineralogy 4 weeks ago
    Mineral monday is moving on to the oxides! An oxide mineral is a mineral based on closely packed oxygen atoms (the oxide anion, O2-) that has metal or semimetal atoms in the interstitial spaces. Oxides can be grouped as simple oxides, with one metal, or multiple oxides, with at least two metals. The varied minerals within the oxide class have widely differing physical properties and appearance, but in general tend to be hard and lustrous, and are generally stable under geologic conditions and in the collector’s cabinet. Many oxides are economically significant, and some can be cut into lovely gemstones. Fun fact: Ice (yes, frozen water) and quartz are both technically oxides! They are usually categorized differently due to their unique qualities. ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the oxides!  #oxides   #minerals   #mineralcollecting   #crystals   #geologyrocks   #mineralogy   #science   #chemistry   #earthscience   #mineralcollector   #rocksandminerals   #geologygeek   #earthtreasures 
  • by friendsofmineralogy 1 month ago
    June is safety month! As more people get outside during the summer months and go look for rocks, it’s a great time for a safety refresher. Put safety to the top of mind while you are planning an excursion, and think about what you are likely to encounter and what makes sense to get you back home in one piece. The mineral collector in our image is on an underground expedition, and has realized she will be on hands and knees in dark spaces – her helmet, knee pads, long sleeves, and heavy boots and gloves will protect head, skin and joints. She is sitting and inspecting finds and has removed the eye protection she might need when doing heavy hammering on rocks. If our mineral collector was instead standing in a quarry, the safety equipment needed might be slightly different – no need for knee pads, for instance. If browsing for agates in an open stream, quite different entirely – no heavy gear, but secure waterproof footwear. The point is to be thoughtful and aware of the situations and environment you are likely to encounter and to be prepared. Preparation doesn’t just mean gear for preventing an injury. It also means having the knowledge for what to do when something does go wrong. Pack a first aid kit and take a first aid course, and know how to get help if needed. If you plan expeditions far from emergency services, consider a wilderness first aid course from an organization like NOLS. And it can not be overstated: beware of ledges above you! A beach bluff or rock ledge may look stable, but can come down in an instant. Come home safe! What are your best safety tips? Photo: Erin Delventhal  #safety   #mining   #rockhound   #community   #minerals   #mineralcollecting   #geology   #crystals   #mineralogy   #geologyrocks   #earthscience   #rocksandminerals   #geologygeek   #earthtreasures 
  • by friendsofmineralogy 1 month ago
    Miargyrite (silver antimony sulfide) is named from the Greek word meyon meaning "smaller" and argyros, meaning "silver." Why “smaller”? It’s not so much that the crystals of miargyrite is really smaller than other silver sulfide minerals (though that is quite often the case), it is more that the silver content is lower than other silver sulfides like pyrargyrite. The example pictured is unusually fine for the species, with a lovely iridescent sheen and ‘rosette’ form. This post finishes up our long  #mineralmonday  romp through the sulfides. There are many more lesser-known sulfide minerals that were not featured in the Pough Field Guide, and perhaps some of those will be subjects for another day. In the meantime, we’re pleased to begin moving on to the next group shortly: the oxides! : Rob Lavinsky & irocks.com.  @arkenstone_minerals  Crystals to 2 cm. San Genaro Mine, Castrovirreyna, Huancavelica, Peru ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the sulfides!  #sulfides   #sulfosalt   #miargyrite   #minerals   #crystals   #geologyrocks   #mineralogy 
  • by friendsofmineralogy 1 month ago
    An 1899 photograph taken at Chicago’s Field Columbian Museum beckons a visitor past the meteorites into the systematic mineralogy gallery. What is “systematic” mineralogy? In the 18th to 19th centuries, at the same time that western naturalists were discovering new-to-them plants and animals and creating detailed taxonomic arrangements of living species into related groups, many scientists were extending these principles of classification to the mineral world. The “system” is a classification of minerals by properties. While you could classify a group of minerals using a wide variety of properties like crystal shape, hardness, etc., the science evolved to determine that classification by chemical composition was the most predictable and useful. James Dwight Dana first published his System of Mineralogy in 1837 with classification based on important chemical groups and structure. Modern classification systems have grown out of Dana’s original system. Today, the International Mineralogical Association (IMA) is the standard body for the definition and nomenclature of mineral species. The IMA currently recognizes 5,780 official mineral species, with more added each year. The generally recognized classes include: native elements, sulfides, sulfosalts, oxides and hydroxides, halides, carbonates, nitrates and borates, sulfates, chromates, molybdates and tungstates, phosphates, arsenates and vanadates, and silicates. Systematic collections were popular among hobbists for many years. Today systematic holdings in museums are important repositories of the science, and there are still many collectors who search out rare species for a systematic collection, but the fashion (and the sheer number of officially recognized species) means that most hobbyist collectors focus their personal collecting framework with different objectives, perhaps focusing on a specific species or region or a certain aesthetic.  #systematicminerals   #mineralcollection   #history   #science   #minerals   #geology   #crystals   #geologyrocks   #mineralogy   #earthscience   #mineralcollector   #rocksandminerals   #geologygeek   #earthtreasures   #cabinetofcuriosities 
  • by friendsofmineralogy 1 month ago
    Jamesonite (lead iron antimony sulfide) can form in masses of hairlike crystals like boulangerite and is sometimes called “feather ore” along with boulangerite and a few related uncommon minerals that are difficult to distinguish, but it can also form in thicker crystals that appear similar to stibnite like the fine example pictured. That’s not for no reason– stibnite is antimony sulfide (Sb2S3), and jamesonite has interconnected SbS3 groups: cousins, of a sort. Jamesonite was named after Robert Jameson, University of Edinburgh professor from 1804 until his death in 1854. Jameson was an influential and prolific mineralogist and geologist and taught many famous scientists of the age, even if his lectures were sometimes considered dry. Charles Darwin (yes, *that* Darwin) reportedly said that Jameson’s lectures inspired him "never to attend to the study of geology." Alas. Seems like it worked out okay for him anyway. : Rob Lavinsky & irocks.com.  @arkenstone_minerals  Crystals to 2.3 cm. Concepción del Oro, Municipio de Concepción del Oro, Zacatecas, Mexico ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the sulfides!  #sulfides   #sulfosalt   #jamesonite   #minerals   #crystals   #geologyrocks   #mineralogy 
  • by friendsofmineralogy 2 months ago
    After a pause of a couple of years, in-person mineral shows are returning to many areas! While we have been grateful for the many on-line options, we hope you are able to attend your local show and resume the long history of buying minerals for your collection in a hands-on way. The first slide is a portion of the 1883 painting Der Mineraloge (The Mineralogist) by Raphael Ritz. The central figure is thought to be German mineralogist Gerhard vom Rath (1830-1888), examining mineral specimens from a nearby quarry in a house in Binn, Switzerland. Rath is carefully examining pieces arrayed on tables around the room, deciding which are worthy of taking home for further study, and the woman and child are likely local miner's family members have brought a variety of local mineral specimens to this room expressly for Rath (and other interested buyers or dealers) to see. In turn, Rath or other dealers will then take those pieces out to yet more customers. This is not unlike how many mineral specimens still make it to modern-day collectors. The general scene from the 1883 painting is also similar to that seen at every modern day mineral show. In the second slide, a snapshot from a 2018 show in Farmington, New Mexico, a friendly dealer is giving a short tutorial on mineral science to an interested family of new collectors. Perhaps this dealer collected some of his pieces himself, but undoubtedly some of them were obtained from other sources, and now he has arrayed them in an attractive table display. He understands the importance of sharing his knowledge with new audiences-- so that they might someday become customers, sure, but more importantly so that they share in his enthusiasm for these amazing objects. Slide 2 Photo Credit: Erin Delventhal  #history   #art   #community   #minerals   #mineralcollecting   #geology   #crystals   #mineralogy   #geologyrocks 
  • by friendsofmineralogy 2 months ago
    There are just a few sulfide minerals that can form as fibrous masses, that look almost like hair growing on a rock matrix. Boulangerite (lead antimony sulfide) is one of them. Boulangerite is easily mistaken for jamesonite, which we’ll discuss next week, but is a little less brittle. The thinner crystals of boulangerite are even a little flexible. Boulangerite melts at the (relatively) low temperature of 525 °C. For a little context, it is often found in association with minerals like calcite, which melts at 1339 °C, and other sulfide minerals like sphalerite, which melts at 1827 °C. Because it therefore also crystallizes at lower temperatures than those associated minerals, presence of minerals like boulangerite is evidence of changing conditions within the earth--in this case, later low to moderate temperature hydrothermal veins interacting with older host rocks. Boulangerite was named after French mining engineer Charles Louis Boulanger, who first analyzed this species in 1835 and calling it "plomb antimonie sulfure." : Rob Lavinsky & irocks.com.  @arkenstone_minerals  Crystals to 1.5 cm. Noche Buena Mine, Noche Buena, Municipio de Mazapil, Zacatecas, Mexico ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the sulfides!  #sulfides   #sulfosalt   #boulangerite   #minerals   #crystals   #geologyrocks   #mineralogy 
  • by friendsofmineralogy 2 months ago
    Quartz twin laws can be divided into two categories: inclined axes laws (very rare) and parallel axes laws (very common). All inclined axes laws are contact twins. Of the inclined axes laws, the Japan law is the most common – the others are so rare that we’re covering all of them in one post. Frondel (1962) describes 15 inclined axes laws in α-quartz and 9 laws in β-quartz* (some correspond to twin laws in α-quartz). The α-quartz laws can be further categorized into three types: 1) a pair of coplanar prism faces with the c-axes inclined, as seen in the Japan law twin, 2) a pair of coplanar rhombohedral faces with an angle of rotation about the normal of the joined face, and 3) a coplanar prism face and a rhombohedral face defined by zonal relations or the angle of rotation about the normal to m (or r). All β-quartz laws fall within the first category except for the Samshvildo Law (the validity of which is debated). Several twins have also been postulated to exist based on probable crystallographic geometries. The Reichenstein-Griserntal (RG) Law is one of the few of these enigmatic twin laws that you might find a photo example of. The Reichenstein (R) Law was first described in 1851 but was then dismissed as oriented growths on calcite. In 1905 the Grieserntal (G) Law was described and eventually accepted as a genuine twin – though technology has advanced to allow observation at an atomic level, common practice requires that a twinning law must have statistical proof that the geometry in question occurs more often than just by chance. Note that the angles of inclination of the R and G twin are supplementary. All twins in category 1 will have a second supplementary angle that adheres to the same law, though the RG twin is seen in both angles more often than its counterparts. *See our previous post about the Cumberland habit for more about β-quartz. : Eric He  @eric8he  of  @southforkminerals , specimen from King County, Washington. Crystal drawings from Goldschmidt’s Atlas der Krystallformen, Drugman (1921 and 1927), and modified from renderings by Amir Ahkavan. Graphics by Erin Delventhal.
  • by friendsofmineralogy 2 months ago
    Bournonite (lead copper trithioantimoniate) wasn't always called bournonite. Jacques Louis, Comte de Bournon described it in 1804. Comte de Bournon called it endellione after the the location it was found: St Endellion in Cornwall, England. It was renamed after Bournon in 1805. The distinctive 'cogwheel' shapes of bournonite crystals are the result of twinning, with the twin plane on a face of the prism. The angle between the faces is not quite a right angle (around 86 degrees) so groups of these crystals may have the rough appearance of a cogwheel. Romanian miners used to call it Rädelerz – "wheel-ore." : Rob Lavinsky & irocks.com.  @arkenstone_minerals  Crystals to 5 cm. Les Malines District, Saint-Laurent-le-Minier, Gard, Languedoc-Roussillon, France ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the sulfides!  #sulfides   #sulfosalt   #bournonite   #minerals   #crystals   #geologyrocks   #mineralogy 
  • by friendsofmineralogy 2 months ago
    The most recognizable quartz twin is the Japan law twin. When originally discovered in La Gardette, France, specimens were labeled as La Gardette twins, but after an abundant number of specimens from the Otome mining district in Japan reached Europe in 1895, Victor Goldschmidt named the law after Japan. The latter name has stuck. The Japan law twin is a contact twin in which the two crystals are reflected across a plane so that the c-axes are inclined away from each other at 84º33’ – almost 90º, but not quite! The prism (m-) faces perpendicular to the composition plane (the front and back) are parallel (pro tip: checking if these faces are parallel is one of the easiest ways to rule out a possible Japan law twin). Japan law twins often show similarly sized crystals and/or a tabular (flattened) habit, but not always. Depending on the degree of crystal development, the twin may take several outward appearances. On one far end of the range, the twin may appear as two distinct crystals with a clear notch in between (often called an “open twin,” like the lower left specimen in the first image); on the other far end, it may be hard to distinguish the two crystals and the notch might not be more than a slight divot (often called a “closed twin,” like the lower right specimen in the first image). Some Japan law twins appear heart-shaped, which falls somewhere in the middle. In all these cases and more (see the fourth slide!), the angle between the two twinned crystals remains constant. Japan law twins are found in many worldwide localities and can feature a multitude of other qualities associated with quartz, including the habits we’ve discussed previously, as well as coloration (amethyst, smoky, etc.), and sceptering. : clockwise from top left: Rock Currier, specimen from Otume Mine, Japan; Rob Lavinsky & irocks.com  @arkenstone_minerals , crystals from Mina Tiro Estrella, New Mexico, USA; Washington Camp, Arizona, USA; and Vera Cruz, Mexico. Crystal drawings from Goldschmidt’s Atlas der Krystallformen. Graphics by Erin Delventhal.  #quartz   #quartzcrystal   #japanlawtwin   #crystallography   #minerals   #mineralspecimens   #mineralcollector   #rocksandminerals   #mineralsofig 
  • by friendsofmineralogy 2 months ago
    Enargite (copper arsenic sulfosalt) usually is a dark massive material, but it can occur as well-defined tabular or prismatic metallic crystals. It is found in hydrothermal vein deposits with other sulfide ore minerals. Because enargite crystals have perfect cleavage in one direction, they were named from the Greek word enarge, meaning "distinct" or "apparent." This aesthetic cluster of enargite crystals is quite unusual and demostrates again that dark minerals can be beautiful. We have one month left of sulfide and sulfosalt minerals! What do you think is next? : Rob Lavinsky & irocks.com  @arkenstone_minerals  Crystals to 1.3 cm. Quiruvilca Mine, La Libertad, Peru ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the sulfides!  #sulfides   #sulfosalt   #enargite   #minerals   #crystals   #geologyrocks   #mineralogy 
  • by friendsofmineralogy 2 months ago
    The next segment of our quartz crystallography series will be discussing quartz twinning, but before we can discuss twins, we need to define “twinning”. Twinning refers to instances when two (or more) crystals are growing in a fixed relationship to one another. This is not multiple crystals growing together at random but specific geometries dictated by the internal structure of a mineral species. Each mineral species is composed of a specific internal arrangement (a crystallographic structure) of a specific set of elements (a defined chemical composition). The arrangement of these internal atoms, ions, or molecules dictates what is described as the crystal lattice, which has axes and angles between each set of axes that defines its presence in three-dimensional space. The crystal lattice controls what geometries (if any) are possible in twinning. Many different minerals can be twinned, but each mineral has a strict limit to the number of geometrical forms created by twinning – a specific instance is called a twin law. The crystals twinned by a specific twin law will ALWAYS take an identical position relative to each other. A twin law is defined by a transformation (a reflection, rotation, or inversion) about an additional symmetry element (a plane, axis, or point) that is absent in a single crystal. The surface between two twinned crystals is the composition surface. Twinned crystals are usually described as a contact twin or a penetration twin. A contact twin has a set composition surface, often a plane, which might look like a single crystal was cut, transformed, then stuck back together, while a penetration twin has an irregular composition surface that may look like two crystals, one transformed, then smushed together. Most quartz is twinned, but not in the way you might think – not all twinning relationships are visible externally. More about that later! : Rob Lavinsky & irocks.com  @arkenstone_minerals  with graphics by Erin Delventhal.  #quartz   #quartzcrystal   #twincrystal   #minerals   #mineralspecimens   #mineralsofig   #mineralcollector   #crystals   #crystallography   #crystalsofig   #science   #rocksandminerals   #themoreyouknow   #instacrystals   #ilikerocks 
  • by friendsofmineralogy 2 months ago
    Tennantite was named in honor of Smithson Tennant, an English chemist who discovered the elements osmium and iridium. Tennantite is closely related to tetrahedrite, but where tetrahedrite has antimony, tennantite has arsenic. It can (and does) form a series with tetrahedrite, and also has it's own subgroup within the tetrahedrite group because of the varying end-members possible in the "X" cation constituent in the formula, including iron, zinc, copper, and mercury. Fun fact: The metal smelted from tennantite is a copper-arsenic alloy that is harder than pure copper. Archeological studies have found that arsenical coppers were in much wider use than previously realized. So, it is is likely that smelting tennantite and similar ores helped the ancients make discoveries and significant steps in knowledge and progress that helped bring on the Bronze Age. : Rob Lavinsky & irocks.com  @arkenstone_minerals  Crystals to 4.5 cm. Tsumeb, Otjikoto (Oshikoto) Region, Namibia ICYMI: Each  #mineralmonday  we present a mineral species with some history and science, following along the order presented in Frederick Pough's definitive Field Guide to Rocks and Minerals; currently working through the sulfides!  #sulfides   #sulfosalt   #tennantite   #minerals   #crystals   #geologyrocks   #mineralogy 
  • by friendsofmineralogy 2 months ago
    Quartz crystals don't have hands, but can still be right-handed and left-handed. Unlike humans, one isn't really more common than the other. Handedness is a result of the tetrahedral shape of the quartz SiO4 atomic "building block." These tetrahedral blocks form helical chains that can spiral in either direction, resulting in two mirror-image options for symmetry: left- and right-handed crystals. How can you tell if a given quartz point is right- or left-handed? Often, you can't. Two of the more unusual quartz forms (the trigonal trapezohedron and the trigonal bipyramid) can result in faces (called x or s, respectively) that will indicate the handedness of a crystal. The position of the x- and/or s-faces in relation to the r-faces reveals the handedness of the structure of the crystal. Our image shows two matched, mirror-image Arkansas quartz points with s-faces. When the s-face is present to the left of the r-face, it is a left-handed crystal; when the s-face is to the right of the r-face, it is a right-handed crystal. Even with well developed x- or s-faces, determining handedness can be difficult! Quartz crystals don't show a preference for one direction or the other, and both 'hands' can and do show up in the same deposits, so why do we bring it up? Because handedness is an important feature in determining some types of twinning habits, coming soon! FM photo by Jessica Robertson with graphics by Erin Delventhal. Many thanks to The Quartz Page www.quartzpage.de for technical guidance. Check them out for more!