Minerals.net

Acanthite is composed mostly of silver, and is its most important ore . nbsp Acanthit...  More

Acanthite is composed mostly of silver, and is its most important ore. Acanthite and Argentite are usually grouped together in mineral guides as one mineral. However, they are scientifically recognized as two unique minerals, even though they are composed of the same substance. They only differ in crystal structure. As explained below in more detail, Argentite cannot exist at normal temperatures. Specimens labeled as Argentite are sometimes sold by dealers, however, these specimens are really Acanthite pseudomorphs after Argentite.  Hide

Actinolite and Tremolite are two very similar minerals that form a series with each o...  More

Actinolite and Tremolite are two very similar minerals that form a series with each other and essentially share the same chemical formula. Actinolite has a greater presence of iron over magnesium, whereas Tremolite has a greater presence of magnesium over iron.

The green color of Actinolite is produced by the iron in its chemical structure. The amount of iron varies among specimens, causing different contrasts of green. More iron will give a specimen a darker color.

Actinolite sometimes occurs as thin, splintery inclusions inside Quartz crystals. If the inclusions are parallel and dense, it will cause chatoyancy in the Quartz.

Actinolite and Tremolite share several recognized varieties. Mountain Leather, a thickly fibrous and leathery variety, has a silky luster, a soft felt-like feel, and elastic fibers. Nephrite, another fibrous variety, is made up of tough, interlocking fibers, so dense that the fibers are not discernible. Translucent Nephrite with a uniform or interesting color distribution that is extremely tough fits under the category of Jade.

Actinolite and Tremolite both contain a form of asbestos which is made of movable and elastic fibers. Actinolite asbestos is less common; most forms are in fact Tremolite. This form of the mineral contains significant health hazards and is further discussed in the Tremolite mineral detail page.
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Adamite occurs in many different lively colors. Different impurities are responsible ...  More

Adamite occurs in many different lively colors. Different impurities are responsible for the color types. When copper is present in Adamite, this gives a vibrant green or blue color, and when cobalt is present, it gives a pink to purple color. Some impurities such as copper prevent the Adamite from its habit of being fluorescent.

Adamite crystals are usually embedded in rusting, crumbly, brown Limonite matrix that stain the hands. Since the Limonite crumbles when scrubbed, care must be exercised when washing such specimens.
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Aegirine is a member of the pyroxene group , and forms a series with the mineral Augi...  More

Aegirine is a member of the pyroxene group, and forms a series with the mineral Augite. It is well known for its long slender crystals with very distinctive terminations, and some of the more lustrous forms of this mineral are true classics. Aegirine was named by Norweigan mineralogist Hans Morten Thrane Esmark (1801–1882). Esmark named this mineral after Aegir, a mythical Norse sea god, in recognition of the discovery of Aegirine near the sea.
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Afghanite is a rare and coveted mineral with a striking blue color, first identified ...  More

Afghanite is a rare and coveted mineral with a striking blue color, first identified in 1968. With a very close resemblance to Lazurite, and occurring together in the same deposits, Afghanite is distinguished by its unique crystal habit. Afghanite is named after its most significant locality in northern Afghanistan.
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Since most forms of Agate are dull and uninteresting until they are cut and polished, we will show images mostly from the cut and polished forms for visual clarity.

Agate is the banded form of the mineral Chalcedony , which is a microcrystalline vari...  More

Agate is the banded form of the mineral Chalcedony, which is a microcrystalline variety of Quartz. Agate is the most varied and popular type of Chalcedony, having many varieties on its own. Although the pattern on every Agate is unique, the locality of an Agate will provide resemblances in banding style and color, thus lending many Agates with a geographic prefix. Some examples are Laguna Agate (named after Ojo Laguna, Mexico) or Botswana Agate (after the African country of Botswana). Other variety names used connote specific colors or patterns, such as Fire Agate or Eye Agate.

Agate usually forms in rounded nodules or knobs which need to be sliced open to bring out the internal pattern hidden in the stone. Most Agate is ugly in its natural state; specimens must be polished to bring out their full beauty. Much of the Agate sold to collectors has been treated, in the form of tumbled stones or polished slabs. Popular collector forms of Agate include nodules or geodes sliced in the middle into two polished cross-sections, or thin slabs from nodule or geode cross-sections.

The formation of Agate is most often from deposition of layers of silica filling voids in volcanic vesicles or other cavities. The layers form in stages with some of new layers providing an alternating color. Since the cavities are irregularly and uniquely shaped, each Agate forms its own pattern based on the original cavity shape. When a cavity is completely filled, it forms a solid mass of Agate, but often it is only partially filled, leaving a hollow void which often has crystalline Quartz growths on its innermost layer. This is the cause of Agate forming the outer lining of most geodes.

Agate is often dyed to enhance its colors. This is especially true of Agate from Brazil. Bright neon colors such as bright blue and red are rarely natural.

Agate is named after the Achates River (now known as the Dirillo River) on the island of Sicily, Italy, whose upper waters were an ancient source of this gemstone.

For additional information, see the gemstone section on Agate.
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div Alabandite is an uncommon sulfide with a fairly simple chemical formula . It was ...  More

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Albite belongs to the Plagioclase Feldspar group, an isomorphous solid solution serie...  More

Albite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series. Albite is one end member, containing sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium. The intermediary members are Oligoclase, Andesine, Labradorite, and Bytownite. Oligoclase and Andesine are considered by some to be a variety of Albite rather then a separate mineral. The acclaimed Dana's System of Mineralogy lists these intermediary members as individual minerals, whereas the IMA does not recognize them as individual mineral species.

Albite also forms a series with Sanidine, and the intermediary member of this series is Anorthoclase. Albite can contain up to ten percent potassium replacing the sodium. If more than ten percent replaces the sodium, the mineral is no longer Albite, but Anorthoclase.

Albite is a very common mineral, and is an important rock-forming mineral. It takes a longer time for Albite to crystallize than the other feldspars. This enables Albite to form in large and well crystallized examples. Albite is also a common accessory mineral to many rare and unusual minerals. The iridescent variety Peristerite sometimes exhibits an adularescent sheen. This produces an unusual form of Moonstone.

Albite sometimes forms in association with the feldspar mineral Microcline in alternating patterns, and forms a feldspar rock known as Perthite.
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Almandine is the most common member of the Garnet group. It is also a popular gemston...  More

Almandine is the most common member of the Garnet group. It is also a popular gemstone and the most widely used Garnet in the gem trade. More gemstones are faceted from Almandine than any other type of Garnet. Only a small amount of Almandine crystals are transparent and light enough for gemstone use; most of the Almandine found is rough and opaque and not gem quality. Some Almandine Garnets display asterism when polished as cabochons, and are known as "Star Garnets".

Almandine is often embedded in a mica schists, and forms very nice matrix pieces with perfectly formed symmetrical crystals. The schist matrix often breaks up due to weathering, resulting in the Almandine crystals breaking loose into individual, perfectly formed floater crystals which may be quite large.  Hide

Amethyst is a well known mineral and gemstone. It is the purple variety of the minera...  More

Amethyst is a well known mineral and gemstone. It is the purple variety of the mineral Quartz, and its most valuable and prized variety. Its name derives from the Greek "amethystos", which means "not drunken", as Amethyst in antiquity was thought to ward off drunkenness. The color of some Amethyst specimens from certain localities slowly fade upon prolonged exposure to light. When used as a gemstone, Amethyst is often heat treated to deepen the color, or to transform it into Citrine. Some varieties may also change to a light green color, which is given the trade name "Prasiolite", or "Green Amethyst", as it is more commonly known in the gem trade.

Amethyst is most prevalent as small stubby pyramidal crystals, although several localities such as the Mexican occurrences are well-known for producing elegantly tall prismatic crystals, which are very highly regarded by collectors. Amethyst also forms the internal lining of geodes, some of which can be over 10 feet tall and weighing several tons.

For additional information, see the gemstone section on Amethyst.
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Analcime is a member of the zeolite group , and often occurs together with other zeol...  More

Analcime is a member of the zeolite group, and often occurs together with other zeolites. However, it is closely related in structure to the feldspathoid group, and is occasionally also classified as a feldspathoid together with the similar mineral Leucite. However, most mineralogical sources, including the IMA, classify Analcime only as a zeolite and not as a feldspathoid.

Although the crystal structure of Analcime appears isometric, its is usually off by only a fraction of an angle. This technically removes its classification from the isometric crystal system. Analyses of different Analcime crystals have yielded multiple results in crystal symmetry, with the most prevalent symmetry being tetragonal. However, truly isometric examples have been analyzed and do exist, thus making this mineral complex in its crystal classification. Due to Analcime's appearance as an isometric mineral, and the fact that isometric examples do exist, we have placed this mineral within the isometric group for classification.

The name Analcime is derived from the Greek term "an alkimos", meaning "not strong, in allusion to the weak pyroelectricity exhibited by this mineral.
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Anatase is a relatively uncommon yet very aesthetic form of titanium dioxide. It form...  More

Anatase is a relatively uncommon yet very aesthetic form of titanium dioxide. It forms distinct and unique crystals, which are usually microscopic to very small, though a few localities have produced larger crystals. Anatase is polymorphous with the more common Rutile, as well as Brookite. It is often replaced entirely by Rutile, forming interestingly shaped Rutile pseudomorphs after Anatase. The name Anatase is derived from the Greek word anatasis, which means elongation, in allusion to its elongated crystal habit (in relation to Rutile.)
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div Andalusite is known for its interesting variety Chiastolite , which contains a di...  More

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Andesine was named after its original occurrence in the Andes Mountains of South Amer...  More

Andesine was named after its original occurrence in the Andes Mountains of South America. Andesine belongs to the Plagioclase Feldspar group, an isomorphous solid solution series. Albite is one member, containing sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium. Andesine is an intermediary member of this series. Andesine is considered by some authorities as a variety of Albite rather than a separate mineral. The acclaimed Dana's System of Mineralogy lists Andesine as an individual mineral, whereas the IMA does not recognize it as individual mineral species, but rather a calcium-rich variety of Albite. Andesine is the primary feldspar constituent of the igneous rock Andesite.
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Andradite is a member of the Garnet group, and although not as well known as other Ga...  More

Andradite is a member of the Garnet group, and although not as well-known as other Garnets such as Almandine or Pyrope, it is still fairly abundant and can produce fine Garnet gemstones. A valuable gem form of Andradite is the rare Demantoid, which is a transparent green variety that is highly lustrous with an adamantine luster. Andradite is named in honor of José Bonifácio de Andrada e Silva (1763-1838), a Brazilian mineralogist, statesman, professor, and poet, famous for his discovery of Andradite as well as several other important minerals such as Spodumene.  Hide

Anglesite is a secondary lead mineral that always forms through the alteration of lea...  More

Anglesite is a secondary lead mineral that always forms through the alteration of lead sulfides, primarily Galena. Anglesite crystals may contain impurities of Galena, giving a specimen a gray to black color. In some localities, Anglesite forms as a pseudomorph after Galena, giving the crystals a false isometric form.

Gray and black banding is present in some massive Anglesite specimens, which can be seen when a specimen is polished or sliced. Such specimens may even contain unaltered Galena in the center, which did not change over to Anglesite when the outer layers altered. An amber-red Anglesite from Touissit, Morocco, has been synthetically colored by immersing light yellow crystals in bleach.  Hide

Anhydrite is not a common mineral, as it easily alter s to the much more common miner...  More

Anhydrite is not a common mineral, as it easily alters to the much more common mineral Gypsum from the addition of water into its chemical structure. Anhydrite and Gypsum are chemically similar, except Gypsum has the addition of water. In fact, the name of Anhydrite is derived from "An" and "Hydra" - meaning "without water" - in reference to its similarity to Gypsum but the fact that it lacks water. Some specimens only partly alter to Gypsum, leaving one part Anhydrite and the other part Gypsum. Many deposits that once contained much Anhydrite now contain an abundance of Gypsum which was formed by the alteration of the Anhydrite.

Anhydrite also exists as a relic of the past in several traprock occurrences, where the Anydrite dissolves and leaves a hollow cast around its original form. Epimorphs of Quartz and Prehnite over Anhydrite frequently form at certain localities, with the original Anhydrite totally replaced or dissolved.

Anhydrite sometimes occurs in arid regions, forming from the dehydration of Gypsum. Fine but usually small crystals may come from the rock area above salt domes, where the domes absorb all underground water and prevent it from entering the structure of the Anhydrite, which would otherwise cause it to alter to Gypsum. Anhydrite specimens in a collection may also alter to Gypsum if kept in moist conditions over a prolonged period of time.  Hide

Annabergite is a rare nickel mineral that can often has a bright green color. It is t...  More

Annabergite is a rare nickel mineral that can often has a bright green color. It is the end member of a series with Erythrite, with Annabergite being the nickel-dominant member and Erythrite being the cobalt-dominant member. Annabergite often contains some cobalt in its structure. The color caused by cobalt will dominate, and will cause some Annabergite to have a purplish color even if there is less cobalt than nickel present. Annabergite is named after the locality of Annaberg, Saxony, Germany, which is a type locality for this mineral.
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Anorthite belongs to the Plagioclase Feldspar group , an isomorphous solid solution s...  More

Anorthite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series. Albite is one end member, containing sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium. The intermediary members are Oligoclase, Andesine, Labradorite, and Bytownite. Labradorite and Bytownite are considered by some to be a variety of Anorthite rather then a separate mineral. The acclaimed Dana's System of Mineralogy lists these intermediary members as individual minerals, whereas the IMA does not recognize them as individual mineral species.
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Anorthoclase is the intermediary member of the Albite Sanidine series . It is interes...  More

Anorthoclase is the intermediary member of the Albite-Sanidine series. It is interesting to note that this mineral series contains two end members crystallizing in different crystal systems. Albite crystallizes in the triclinic system, whereas Sanidine crystallizes in the monoclinic system.

When Anorthoclase forms, its atoms form in a specific arrangement. This arrangement of the atoms forms the crystal structure of the mineral. Depending on the environment it forms in, it will either form a monoclinic or triclinic crystal. If it forms a monoclinic crystal, it leans toward Sanidine in regard to its crystal structure, and if it forms in the triclinic system, it leans toward Albite. (For this reason, Anorthoclase crystals can either be triclinic or monoclinic, although the tendency is usually toward triclinic.) The scientific classification of Sanidine, Anorthoclase, and Albite can only be determined with x-ray analysis. However, certain localities produce known examples of these particular Feldspars, in which case the mineral type can be determined without complex analysis. (Click here for more detailed information on the crystal structure of the Feldspars.)
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Antimony is a native element that can occur in a natural state, but it is rarely pure...  More

Antimony is a native element that can occur in a natural state, but it is rarely pure. It almost always contains some arsenic, and may also contain traces of silver, iron, and sulfur. On a fresh or preserved surface, Antimony has a tin-white color with a slight blue tinge. Otherwise, it is dark gray due to tarnish. Specimens of native Antimony are usually rather dull and ugly, as they usually lack crystals and have a somewhat dull, tarnished surface.

Antimony and Arsenic are almost identical. In many instances, the only way to tell them apart is by conducting complex scientific tests. Stibarsen, a mixture of arsenic and antimony, is also indistinguishable through common methods.  Hide

div Apatite is named for the Greek word i apate i , which means deceit , since Apatit...  More

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Apophyllite can be a beautiful mineral, forming in lustrous, transparent crystals tha...  More

Apophyllite can be a beautiful mineral, forming in lustrous, transparent crystals that are well-formed and occasionally very large. Though it is found worldwide in volcanic zeolite environments, the Indian traprock quarries have produced enormous quantities of this mineral in all different shapes, sizes, and colors, making Apophyllite easily obtainable and very affordable.

Apophyllite was originally regarded as a single mineral, with a variable ratio of fluorine to hydroxyl. In 1978, the IMA sub-classified into two distinct minerals: Fluorapophyllite and Hydroxyapophyllite. In 1981, an additional rare member with sodium replacing the potassium was added to the group, and called Natroapophyllite.

In a controversial move, the IMA has recently changed the scientific naming of these minerals for easier cataloging and alphabetical indexing. The new mineral names are Apophyllite-(KF) [instead of Fluorapophyllite], Apophyllite-(KOH) [instead of Hydroxyapophyllite], and Apophyllite-(NaF) [instead of Natroapophyllite]. Although use of the original names is now discouraged by the IMA, these names are still used and referenced, with the new names frowned upon by many collectors. The reality is that most collectors rarely sub-classify Apophyllite specimens, and simply label them all as Apophyllite.

Apophyllite-(KF) is the most common and abundant of the group. Most specimens labelled simply as "Apophyllite" are of the Apophyllite-(KF) form. Apophyllite-(KOH) is less common, but is still the dominating form of Apophyllite in several localities, including most of the Virginia occurrences. Apophyllite-(NaF) is very rare, and is found sparingly at only a few localities.

Apophyllite almost always occurs together with zeolites, especially in traprock environments. Apophyllite appears very similar to the zeolites, and is sometimes even confused with them. However, the physical structure of Apophyllite is different, with tetrahedrons aligning in sheets as a phyllosilicates, as opposed to the zeolites which are tectosilicates.

Carletonite is a rare blue mineral that is similar to Apophyllite, and it only occurs in Mont Saint Hilaire, Quebec, Canada. Many classify Carletonite as group member within the Apophyllite group.

Apophyllite is named from a combination of the Greek word "apo" - to be off, and "phyllos" - leaf, alluding to the property of this mineral that it exfoliates (flakes apart like a leaf) when heated due to loss of water in its structure.
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Aquamarine is the greenish blue to blue variety of Beryl . It forms in beautiful crys...  More

Aquamarine is the greenish-blue to blue variety of Beryl. It forms in beautiful crystals that can be quite large and totally transparent. Unlike Emerald which usually is flawed or heavily included, Aquamarine can form in stunning flawless crystals, creating some of the most beautiful mineral masterpieces.

Duller or greenish colored stones can be heated to very high temperatures in which they can attain a beautiful sky-blue color. In fact, much of the Aquamarines used as gemstones are actually heat treated.

For additional information, see the gemstone section on Aquamarine.
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Calcium carbonate forms as both Aragonite and Calcite , and these two minerals only d...  More

Calcium carbonate forms as both Aragonite and Calcite, and these two minerals only differ in their crystallization. Calcite, the more common mineral, forms in trigonal crystals, whereas Aragonite forms orthorhombic crystals. On occasion, crystals of Aragonite and Calcite are too small to be individually determined, and it is only possible to distinguish these two minerals with optical or x-ray testing. The true identity of microcrystalline forms of Aragonite or Calcite may also not be known without complex testing, and this can also cause a confusion between these species.

Most large Aragonite crystals are twinned growths of three individual crystals that form pseudohexagonal trillings. Although Aragonite crystallizes in the orthorhombic system, most prismatic crystals are hexagonally shaped due to the twinning. Trillings can be identified by their multi-directional basal striations from each individual member crystal.

Other minerals may form pseudomorphs after Aragonite. A peculiarity of the mineral world is Calcite after Aragonite, which is a pseudomorph after an existing paramorph. Some Aragonite crystals available to collectors are actually Calcite pseudomorphs after Aragonite. A rare but popular pseudomorph is Copper after Aragonite. Aragonite may also contain sand inclusions, which give a specimen a brown color.  Hide

Arfvedsonite was first discovered in 1823. It is named after Johan August Arfwedson 1...  More

Arfvedsonite was first discovered in 1823. It is named after Johan August Arfwedson (1792–1841), a Swedish chemist credited with the discovery of the element lithium. Arfvedsonite is not a common mineral, and is found only in a limited amount of localities throughout the world. However, several of these deposits have produced outstanding examples of this mineral, making it a very collectible species. There are several variations of Arfvedsonite with different elemental substitutions. Some of these are recognized as individual minerals, thereby making Arfvedsonite a mineral group, with Arfvedsonite the dominating member.  Hide

Arsenic almost always contains some antimony . Nickel, silver, iron, and sulfur are a...  More

Arsenic almost always contains some antimony. Nickel, silver, iron, and sulfur are also commonly found in a given specimen. On a fresh or preserved surface, Arsenic has a tin-white color, but otherwise tarnishes dark gray.

Arsenic and Antimony are almost identical. In many instances, the only way to tell them apart is by conducting complex scientific tests. Stibarsen, a mixture of arsenic and antimony, is also indistinguishable through common methods.

Arsenic is poisonous, and therefore hands should be washed after handling specimens. Fumes are highly toxic, and should never be breathed.  Hide

Arsenopyrite is the most prevalent mineral containing the element arsenic. It forms v...  More

Arsenopyrite is the most prevalent mineral containing the element arsenic. It forms very distinct crystals, which can be large and beautifully formed. Arsenopyrite sometimes tarnishes, forming a colorful iridescent layer.
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Augite is isomorphous with the minerals Diopside and Hedenbergite . It is an intermed...  More

Augite is isomorphous with the minerals Diopside and Hedenbergite. It is an intermediary member between these minerals, forming a series, but contains additional sodium and aluminum within its chemical structure. Strictly speaking, because of the variables in its chemical structure, Augite is really more of a group then a single mineral, but it is still classified a single mineral species by the IMA.

Augite is an important rock-forming mineral, and large crystals are fairly common. It is the most widespread member of the pyroxene group, and it frequently alters to many other minerals, including Hornblende, Chlorite, and Epidote. When altered to Actinolite, it is often called Uralite.

Augite usually occurs in dull crystals that are ugly and uninteresting. Occasionally, though, it is found in large lustrous crystals which are sought after by mineral collectors. The name Augite is derived from the Greek word augites, "brightness", in reference to the bright luster this mineral occasionally exhibits.  Hide

Aurichalcite has a beautiful pastel color that is very distinctive. In its most typic...  More

Aurichalcite has a beautiful pastel color that is very distinctive. In its most typical form, the tiny fragile crystal needles may rub off when touched, and will often leave a blue residue on a surface. Handling of such specimens should be avoided due to their fragility, and washing Aurichalcite should also be avoided for this reason.  Hide

Axinite is the group name for several closely related minerals Axinite Fe , Axinite M...  More

Axinite is the group name for several closely related minerals: Axinite-(Fe), Axinite-(Mg), Axinite-(Mn), and Tinzenite. Axinite on its own without a sub-designation is not recognized as an individual mineral species by the IMA, although many mineral collectors still refer to it by its traditional name without further classifying the type of Axinite. Most of the known Axinite minerals are of the Axinite-(Fe) type.

Axinite was named in 1787 after the Greek word axine, which means "ax", in allusion to the sharp crystals of this mineral. The individual member types were originally Ferro-axinite, Magnesio-axinite, and Mangan-axinite. These were renamed with a suffix designation for easier cataloging reference by the IMA in 2008.
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Azurite owes its name to its beautiful azure blue color, which makes it a very popula...  More

Azurite owes its name to its beautiful azure-blue color, which makes it a very popular and well-known mineral. Large, well-formed, and deep blue crystals from Tsumeb (Namibia), Bisbee (Arizona), and Milpillas (Mexico), make exquisite collector's minerals that are regarded as some of the finest mineral masterpieces in nature.  Hide