Quartz Varieties (Minerals)
Milky Quartz (47)
Milk quartz or milky quartz is the most common variety of crystalline quartz. The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation, making it of little value for optical and quality gemstone applications.
Rose Quartz (48)
Chemical Formula SiO2 Color Pink Hardness 7 Crystal System Hexagonal Refractive Index 1.54 - 1.55 SG 2.63 - 2.65 Transparency Transparent to translucent Double Refraction .009 Luster Vitreous Cleavage Indiscernible Mineral Class Quartz
Agate/Onyx (41)
Chemical Formula SiO2 Composition Silicon dioxide Color Multicolored in banded formation. Colors include white, blue, red, green, yellow, orange, brown, pink, purple, gray, and black. Some rarer forms of Agate are iridescent. Streak White Hardness 7 Crystal System Hexagonal Crystal Forms and Aggregates Agate is a banded microcrystalline form of the mineral Quartz, and does not occur in visible crystals. It occurs in nodules, in massive form, as botryoidal, mammilary, and stalactitic formations, as smooth rounded pebbles, as amygdules, and as the linings of geodes. Transparency Translucent to opaque Specific Gravity 2.6 - 2.7 Luster Vitreous Cleavage None Fracture Conchoidal Tenacity Brittle Other ID Marks 1) Commonly fluorescent, usually green or white. May even show fluorescent banding patterns where some of the bands will fluoresce more strongly than others. 2) Triboluminescent 3) Piezoelectric Complex Tests Dissolves in hydrofluoric acid. In Group Silicates; Tectosilicates; Silica Group Striking Features Banding patterns Environment Agate occurs in all mineral environments, but it is most prevalent in igneous rocks such as basalt. Rock Type Igneous, Sedimentary, Metamorphic
Chalcedony (43)
Chemical Formula SiO2 Composition Silicon dioxide Color White, blue, red, green, yellow, orange, brown, pink, purple, gray, black, colorless, and multicolored. Often banded in many different color combinations, and a few rarer forms are iridescent. Streak White Hardness 7 Crystal System Hexagonal Crystal Forms and Aggregates Chalcedony, being a microcrystalline variety of the mineral Quartz, does not occur in visible crystals. It occurs in botryoidal, mammilary, stalactitic, massive, nodular forms, as smooth rounded pebbles, as banded masses, as amygdules, and as the linings of geodes. Transparency Transparent to opaque Specific Gravity 2.6 - 2.7 Luster Vitreous, waxy, or dull Cleavage None Fracture Conchoidal Tenacity Brittle Other ID Marks 1) Commonly fluorescent, usually green or white. 2) Triboluminescent 3) Piezoelectric Complex Tests Dissolves in hydrofluoric acid In Group Silicates; Tectosilicates; Silica Group Striking Features Hardness and form Environment Occurs in all mineral environments, especially in igneous environments. Rock Type Igneous, Sedimentary, Metamorphic
Citrine (44)
Chemical Formula SiO2 Composition Silicon dioxide Color Yellow, yellow-brown, orange, dark orange-brown, reddish-brown Streak White Hardness 7 Crystal System Hexagonal Crystal Forms and Aggregates Most often as protruding clusters of pyramids on a geode base. Also occurs as short, stubby, terminated crystals, either singular or in drusy aggregates, and occasionally as long prismatic crystals and groupings. Also occurs massive and crusty. Transparency Transparent to translucent Specific Gravity 2.6 - 2.7 Luster Vitreous Cleavage Indiscernible Fracture Conchoidal Tenacity Brittle Complex Tests Soluble in hydrofluoric acid In Group Silicates; Tectosilicates; Silica Group Striking Features Color and crystal habits Environment Occurs in all mineral environments, especially in igneous environments. Rock Type Igneous, Sedimentary, Metamorphic
Jasper (46)
Chemical Formula SiO2 Composition Silicon dioxide, usually with impurities of iron oxides or organic substances. Color Brown, yellow, orange, red, green, or blue. May also refer to any form of opaque Chalcedony in all colors. Jasper is usually multicolored or banded. Streak White Hardness 6.5 - 7 Crystal System Hexagonal Crystal Forms and Aggregates Jasper is a microcrystalline form of the mineral Quartz, and does not occur in visible crystals. It most often is in massive form, but may also be botryoidal, mammilary, and stalactitic formations, as smooth rounded pebbles, and as nodules. Transparency Opaque Specific Gravity 2.7 - 2.7 Luster Vitreous Cleavage None Fracture Conchoidal Tenacity Brittle Other ID Marks 1) Sometimes fluorescent. 2) Triboluminescent 3) Piezoelectric Complex Tests Dissolves in hydrofluoric acid. In Group Silicates; Tectosilicates; Silica Group Striking Features Color habits and hardness Environment Occurs in all mineral environments. Rock Type Igneous, Sedimentary, Metamorphic
Amethyst (42)
Chemical Formula SiO2 Composition Silicon dioxide. Its purple coloring is usually caused by impurities of iron or manganese compounds. Color Light to dark purple. Sometimes banded with purple and whitish lines. May also be mixed together with Citrine. Streak White Hardness 7 Crystal System Hexagonal Crystal Forms and Aggregates Most often as protruding clusters of pyramids on a matrix base. These "pyramids" can be quite large. Also occurs as tall prismatic crystals, as short stubby crystals, in drusy aggregates, massive, in geodes, and as rounded waterworn stones. A very interesting habit is as crystalline crusts inside volcanic pipes. Crystals are usually striated horizontally, and occasionally have a scepter growth. Transparency Transparent to translucent Specific Gravity 2.6 - 2.7 Luster Vitreous Cleavage Indiscernible Fracture Conchoidal Tenacity Brittle Other ID Marks Occasionally fluorescent cream or white in shortwave ultraviolet light. Complex Tests Dissolves in hydrofluoric acid. In Group Silicates; Tectosilicates; Silica Group Striking Features Color, crystal habits, and hardness. Environment Occurs in all mineral environments, especially in igneous environments. Rock Type Igneous, Sedimentary, Metamorphic
Opal (39)
Chemical Formula SiO2 · nH2O Composition Hydrous silicon dioxide. The water can range from 3% to 21% of the total weight, but is usually between 6% to 10%. Color Colorless, white, yellow, orange, red, purple, blue, green, gray, brown, and black. These are some of the base colors of Opal. Certain opals display different colors when viewed from different directions, or when the stone is turned, or when the light source is moved. This phenomenon, called play of color, gives a stone color flashes, or schillers of different colors which vary from stone to stone. Opal also occurs multicolored and banded. Streak White Hardness 4.5 - 6.5 Crystal System Amorphous Crystal Forms and Aggregates Opal is amorphous and does not occur in any crystals, except when it forms as a pseudomorph after another mineral. Opal habits include massive, botryoidal, reniform, stalactitic, earthy, nodular, as veins, in crusts, and in accumulating mounds. It often pseudomorphs after organic matter such as wood, shell, and bone. Transparency Transparent to opaque Specific Gravity 1.98 - 2.25 Luster Usually vitreous, but may also be pearly, waxy, or resinous. Cleavage None Fracture Conchoidal Tenacity Brittle Other ID Marks 1) Rich play of color in some specimens. 2) Often fluoresces, usually bright green; but also light green, light blue, purple, and white. In Group Silicates; Tectosilicates; Silica Group Striking Features Form, hardness, and opalescence Environment Forms in all mineral environments, especially igneous environments. Rock Type Igneous, Sedimentary, Metamorphic
Crystal (45)
Chemistry) a piece of solid substance, such as quartz, with a regular shape in which plane faces intersect at definite angles, due to the regular internal structure of its atoms, ions, or molecules. 2. ( Minerals) a single grain of a crystalline substance. 3.
