Name/Title
Quartz / Sphalerite / ChalcopyriteEntry/Object ID
2009.62.119Description
Chemical Composition: Silicon dioxide
Crystal System: Tetragonal System
Description: Common Name: Quartz / Sphalerite / Chalcopyrite
Chemistry: SiO2 , Silicon dioxide / (Zn, Fe)S, Zinc Iron Sulfide / CuFeS2, Copper Iron Sulfide
Class: Silicates / Sulfides / Sulfides
Location: Huanzala Mine, Peru
Description: Large area of needle-like transparent crystals, with a slight grayish hue, and an area of black opaque crystals, angular in shape, with an intermittent flux of gray and golden granular crystals throughout the specimen.
PHYSICAL CHARACTERISTICS OF QUARTZ:
Color is as variable as the spectrum, but clear quartz is by far the most common color followed by white or cloudy (milky quartz). Purple (Amethyst), pink (Rose Quartz), gray or brown to black (Smoky Quartz) are also common. Cryptocrystalline varieties can be multicolored.
Luster is glassy to vitreous as crystals, while cryptocrystalline forms are usually waxy to dull but can be vitreous.
Transparency: Crystals are transparent to translucent, cryptocrystalline forms can be translucent or opaque.
Crystal System is trigonal; 3 2.
Crystal Habits are again widely variable but the most common habit is hexagonal prisms terminated with a six sided pyramid (actually two rhombohedrons). Three of the six sides of the pyramid may dominate causing the pyramid to be or look three sided. Left and right handed crystals are possible and identifiable only if minor trigonal pyramidal faces are present. Druse forms (crystal lined rock with just the pyramids showing) are also common. Massive forms can be just about any type but common forms include botryoidal, globular, stalactitic, crusts of agate such as lining the interior of a geode and many many more.
Cleavage is very weak in three directions (rhombohedral).
Fracture is conchoidal.
Hardness is 7, less in cryptocrystalline forms.
Specific Gravity is 2.65 or less if cryptocrystalline. (average)
Streak is white.
Other Characteristics: Striations on prism faces run perpendicular to C axis, piezoelectric (see tourmaline) and index of refraction is 1.55.
Associated Minerals are numerous and varied but here are some of the more classic associations of quartz (although any list of associated minerals of quartz is only a partial list): amazonite a variety of microcline, tourmalines especially elbaite, wolframite, pyrite, rutile, zeolites, fluorite, calcite, gold, muscovite, topaz, beryl, hematite and spodumene.
Best Field Indicators are first the fact that it is very common (always assume transparent clear crystals may be quartz), crystal habit, hardness, striations, good conchoidal fracture and lack of good cleavage.
PHYSICAL CHARACTERISTICS OF SPHALERITE:
Color is typically black but can be brown, yellow, reddish, green, and less commonly white or colorless.
Luster is adamantine or resinous or submetallic to earthy in massive forms.
Transparency crystals are transparent to translucent.
Crystal System is isometric; bar 4 3m
Crystal Habits can be complicated with the rhombic dodecahedron, tetrahedron and combinations of these having cubic and tristetrahedron faces giving the crystals multiple faces of often indistinct forms. To add more confusion to the indistinct crystals, twinning is common and sometimes pervasive. Massive forms are common and can be granular, earthy, botryoidal, concretionary and fibrous. An aggregate of botryoidal crusts with layers of wurtzite and galena is called "Schalenblende" is sometimes cut and polished as an ornamental stone.
Cleavage is perfect in six directions forming dodecahedrons.
Fracture is conchoidal, but rarely seen because of frequent cleavage.
Hardness is 3.5-4
Specific Gravity is approximately 4.0 (heavier than average, but light when compared to most metallic minerals)
Streak is yellow to light brown (unusually light colored for a normally dark mineral).
Other Characteristics: Striations on tetrahedral faces, triboluminescent (meaning it may glow if crushed), an index of refraction of 2.37 - 2.42, a dispersion (fire) of 0.156 and finally sphalerite is pyroelectric (meaning that it forms a slight electrical charge when heated or cooled).
Associated Minerals almost always include galena, pyrite, fluorite, chalcopyrite, quartz, calcite, magnetite, pyrrhotite and many others.
Best Field Indicators are crystal habits, streak, cleavage, high luster, softness and twinning
PHYSICAL CHARACTERISTICS OF CHALCOPYRITE;
Color is brassy yellow, tarnishes to irredescent blues, greens, yellows and purples.
Luster is metallic.
Transparency: Crystals are opaque.
Crystal System is tetragonal; bar 4 2m
Crystal Habits are predominantly the disphenoid which is like two opposing wedges and resembles a tetrahedron. Crystals sometines twinned. Also commonly massive, and sometimes botryoidal.
Cleavage is rather poor in one direction.
Fracture is conchoidal and brittle.
Hardness is 3.5-4
Specific Gravity is approximately 4.2 (average for metallic minerals)
Streak is dark green.
Other Characteristics: Some striations on most crystal faces.
Associated Minerals are quartz, fluorite, barite, dolomite, calcite, pentlandite, pyrite and other sulfides.
Best Field Indicators are crystal habit, tarnish, softness and brittleness.
Fracture: conchoidal
Hardness: 7 Quartz
Luster: Glassy
Occurrence: Quartz occurs in hydrothermal veins as gangue along with ore minerals. Large crystals of quartz are found in pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms.
Naturally occurring quartz crystals of extremely high purity, necessary for the crucibles and other equipment used for growing silicon wafers in the semiconductor industry, are expensive and rare. A major mining location for high purity quartz is the Spruce Pine Gem Mine in Spruce Pine, North Carolina.[6]
Rock Type: Sedimentary
Specific Gravity: 2.65
Streak: whiteCollection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationDimensions
Width
7-1/4 inDepth
2-1/4 inLength
6-1/4 inWeight
6.94 ozLocation
Location
Display Case
FS-3-BRoom
Frieda Smith HallBuilding
Crater Rock MuseumCategory
ExhibitMoved By
Jillian Mather KettleyDate
January 29, 2025Notes
Location/ inventory