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Amazonite

Amazonite

Amazonite is a blue-green variety of microcline feldspar. The color is caused by impurities of lead.

Aquamarine with microcline and quartz

Aquamarine with microcline and quartz

Notice the transparent portions of this aquamarine, a variety of beryl. Such clarity is what gem-cutters look for. Virtually all aquamarine gemstones originate in pegmatites. This aquamarine is perched on an exceptionally well-formed microcline crystal.

Beryl (variety: Aquamarine)

Beryl (variety: Aquamarine)

Although these two minerals grew side by side, they have different shapes. The atoms in beryl connect in a six-fold pattern and form six-sided crystals. The atoms in muscovite form layers that make sheet-like crystals.

Beryl (variety: Aquamarine)

Beryl (variety: Aquamarine)

As the name suggests, aquamarine exhibits the colors of the sea. The delicate hues come from traces of iron (mainly Fe+2). Heating removes aquamarines' green tones, leaving a pure blue color. Brazil is the major source of the gem aquamarine.

Beryl (variety: Emerald)

Beryl (variety: Emerald)

This beryl (emerald) was found at the Hiddenite and Emerald Mine, near Stony Point, Alexander County, North Carolina in 1971. It measures 11 cm in depth and is one of the finest emerald specimens ever found in North America. The specimen was given to the Smithsonian Institustion by Dr. Lawrence Funt in 1979.

Beryl (variety: Heliodor)

Beryl (variety: Heliodor)

Golden beryl, or heliodor, gets its name from the Greek words for sun and gift. Iron gives the specimen its yellow glow. Different amounts of iron create a color range that includes green beryl.

Beryl (variety: Morganite on albite)

Beryl (variety: Morganite on albite)

Morganite, the pink variety of beryl, gets its color from impurities of manganese. Like aquamarine, the blue-green variety of beryl, it is used as a gemstone. Morganite is found only in pegmatites. Renowned gemologist George Kunz named it after his patron, financier J. P. Morgan. Madagascar is famous for fine morganite, but most material now comes from Brazil, Pakistan, and the U.S. (California).

Chrysotile Asbestos

Chrysotile Asbestos

Commonly used in brake linings and roofing, chrysotile, or white asbestos, is a member of the serpentine family.

Crocidolite Asbestos

Crocidolite Asbestos

If they are inhaled, needlelike fibers of crocidolite can penetrate deeply into the lungs, making it the most dangerous asbestos mineral. It was once important in shipbuilding but is rarely used today. Known as blue asbestos, crocidolite is a variety of riebeckite.

Cronstedtite

Cronstedtite

Elbaite

Elbaite

Elbaite is a member of the tourmaline family, with a chemical composition of Na(Li,Al)3Al6(BO3)3Si6O18(OH)4. The tourmaline family encompasses eleven minerals all with a ring arrangement of silicon, boron, and oxygen. This blue indicolite elbaite is from Minas Gerais, Brazil, the main source of fine tourmaline crystals.

Elbaite

Elbaite

Elbaite is a member of the tourmaline family, with a chemical composition of Na(Li,Al)3Al6(BO3)3Si6O18(OH)4. The pink variety of elbaite is called rubellite. The tourmaline family encompasses eleven minerals all with a ring arrangement of silicon, boron, and oxygen. All tourmalines have the special property called piezoelectricity. This means that they can acquire an electric charge when struck by an object, or subjected to high pressure, such as the shock wave from an explosion. This elbaite specimen is from Minas Gerais, Brazil, the main source for fine tourmaline crystals.

Elbaite

Elbaite

The tourmaline family encompasses eleven minerals all with a ring arrangement of silicon, boron, and oxygen. Elbaite is a member of the tourmaline family, with a chemical composition of Na(Li,Al)3Al6(BO3)3Si6O18(OH)4. The pink variety of elbaite is called rubellite. All tourmalines have the special property called piezoelectricity. This means that they can acquire an electric charge when struck by an object, or subjected to high pressure, such as the shock wave from an explosion.

Elbaite

Elbaite

The tourmaline family encompasses eleven minerals all with a ring arrangement of silicon, boron, and oxygen. Elbaite is a member of the tourmaline family, with a chemical composition of Na(Li,Al)3Al6(BO3)3Si6O18(OH)4. The pink variety of elbaite is called rubellite. All tourmalines have the special property called piezoelectricity. This means that they can acquire an electric charge when struck by an object, or subjected to high pressure, such as the shock wave from an explosion.

Elbaite

Elbaite

These elbaite crystals are colorless at the tips because the supply of iron impurities decreased while they grew. Manganese impurities incorporated during early stages of growth and colored the interiors pink. The chemical composition of elbaite is Na(Li,Al)3Al6(BO3)3Si6O18(OH)4.

Elbaite

Elbaite

The tourmaline family encompasses eleven minerals all with a ring arrangement of silicon, boron, and oxygen. Elbaite is a member of the tourmaline family, with a chemical composition of Na(Li,Al)3Al6(BO3)3Si6O18(OH)4. The pink variety of elbaite is called rubellite. All tourmalines have the special property called piezoelectricity. This means that they can acquire an electric charge when struck by an object, or subjected to high pressure, such as the shock wave from an explosion.

Elbaite

Elbaite

Elbaite is a member of the tourmaline family, with a chemical composition of Na(Li,Al)3Al6(BO3)3Si6O18(OH)4. The tourmaline family encompasses eleven minerals all with a ring arrangement of silicon, boron, and oxygen.

Elbaite with albite and lepidolite

Elbaite with albite and lepidolite

While these two elbaite crystals were growing, conditions changed. The second growth phase gave rise to thousands of bristly, hair-like crystals. The chemical composition of elbaite is Na(Li,Al)3Al6(BO3)3Si6O18(OH)4.

Elbaite with albite, quartz, microcline

Elbaite with albite, quartz, microcline

Magnificent blue-capped elbaites jut out of a quartz and white-bladed albite base. Elbaite is a member of the tourmaline family. A source of muscovite since the early 20th century, Pederneira Mine is more important for gem tourmalines today.

Elbaite with quartz and albite

Elbaite with quartz and albite

Some people think this specimen, nicknamed "Candelabra," looks like three hot-pink candles in a quartz candelabra. As the elbaite crystals grew, the growth solution changed from manganese-rich to iron-rich, creating a blue top on each candle.

Elpidite with pyrite

Elpidite with pyrite

Glaucophane

Glaucophane

This mineral forms only at the high pressures and low temperatures within subduction zones.

Helvite with quartz and pyrite

Helvite with quartz and pyrite

You can see three generations of growth in this specimen. Clear quartz formed first. The yellow crystal of helvite grew on top, and flecks of brassy pyrite crystallized later.

Hemimorphite

Hemimorphite

Hemimorphite

Hemimorphite

Jadeitite

Jadeitite

Jade, the "gemstone" mined from subduction zones, is really two types of metamorphic rock: nephrite and the rarer jadeitite (shown here). Jade is rare because it forms only along faults deep within active subduction zones. Windows have been polished on this sample to show the rock’s true colors.

Lawsonite

Lawsonite

This mineral forms only at the high pressures and low temperatures within subduction zones.

Liddicoatite

Liddicoatite

The photo shows a slice from a single crystal of liddicoatite, a member of the tourmaline family. The color-zoning reveal the crystal's history, just as the rings in a tree records its past. Crystals may start and stop growing many times. In most cases, there is no way of knowing how long each phase lasted. This particular crystal changed color as it grew. The pink portion of the liddicoatite formed when the solution feeding it was manganese rich. The green part grew when the solution became iron rich.

Mesolite

Mesolite

Each needle on this mesolite specimen is a single crystal. The crystal grew from a water solution that circulated through cooled volcanic rock. They fanned out to fill a cavity left by a gas bubble in the rock. The chemical composition of mesolite is Na2Ca2(Al6Si9)O30.8H2O.

Mesolite (with Apophyllite)

Mesolite (with Apophyllite)

Each needle in this spray of mesolite is a single crystal. The crystals grew from a water solution that circulated through cooled volcanic rock. They fanned out to fill a cavity left by a gas bubble in the rock.

Microcline

Microcline

The blue-green variety of microcline (a feldspar), amazonite is found exclusively in pegmatite deposits. It is popular for use in beads and carvings. The chemical composition of amazonite is AlSi3O8.

Milarite

Milarite

The chemical composition of milarite is (K,Na)Co2(Be,Al)3Si12O30.H2O. The inclusion of silicon (Si) and oxygen (O) in its makeup classifies milarite as a silicate. Nearly one quarter of all minerals are silicates.

Muscovite

Muscovite

Muscovite forms thin, flat crystals that grow to enormous sizes. Pegmatites are the major source of muscovite and other mica species, which are often used for electrical insulation and shingles. The chemical composition of muscovite is KAl2(Si3Al)O10(OH,F)2.

Opal

Opal

This 181.9 carat white opal was found in Coober Pedy, Australia.

Opal

Opal

The cause of the brilliant play of colors in opal was an enigma until relatively recently. Scanning electron microscope studies show that opals consist of transparent spheres of silica that are tightly packed. The voids or spaces between the spheres contain air or water. The regular arrangement of spheres acts as a diffraction grating, breaking visible white light into separate colors. These specimens of opal are still embedded in the surrounding rock, called matrix.

Opal

Opal

The cause of the brilliant play of colors in opal was an enigma until relatively recently. Scanning electron microscope studies show that opals consist of transparent spheres of silica that are tightly packed. The voids or spaces between the spheres contain air or water. The regular arrangement of spheres acts as a diffraction grating, breaking visible white light into separate colors.

Rhodonite

Rhodonite

These exceptionally fine rhodonite crystals get their pink color from manganese. They were recovered from a silver and tungsten mine in Peru.

Spessartine with quartz and muscovite

Spessartine with quartz and muscovite

Reddish-orange spessartine is one of the garnet minerals. Here, it sits on white quartz and plate-like crystals of muscovite. Magnificent pegmatite specimens such as this have been found in Pakistan since the mid-1980s.

Spodumene (variety: Kunzite)

Spodumene (variety: Kunzite)

Although kunzite is the violet or pink variety of the mineral spodumene, light traveling in each direction through a kunzite crystal interacts with the atomic structure to create different colors. Thus, when viewed from different directions, the stone can appear pink, nearly colorless, or green. Additionally, kunzite is an "evening stone", meaning that its color fades with exposure to light. Kunzite is also prone to splitting along weaknesses when cut, making it more suitable for pendants than for rings or bracelets. The stone shown here is one of the largest known gem-quality kunzite crystals.

Sugilite

Sugilite

Sugilite is a violet stone used for jewelry and ornamental objects. Colored by Manganese, it often shows patches of black, brown, and blue lines, creating a unique mottled effect. It was named for Ken-ichi Sugi, the Japanese geologist who discovered it in 1944. This 9.2cm long specimen shows the typical appearance of sugilite.

Topaz

Topaz

Though most people would not recognize this clear mineral as topaz, topaz is usually found either clear or a yellow-brown. The popular blue topaz is not common in nature, but can be made by irradiation and heat treatment of the clear or yellow varieties. The chemical composition of topaz is Al2SiO4(F,OH)2.

Topaz with lepidolite

Topaz with lepidolite

Most topaz come from pegmatites. This large crystal capped with lepidolite is naturally blue. This is rare in nature, however, and most blue topaz is man-made by irradiating and heating colorless or yellow-brown topaz. The chemical composition of topaz is Al2 SiO4(F,OH)2.

Willemite

Willemite


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