Name/Title
Quartz var. AgateEntry/Object ID
2009.62.401Description
Chemical Composition: SiO2
Crystal System: Hexagonal System
Description: Common Name: Agate
Chemistry: SiO2 , Silicon dioxide
Class: Silicates
Location: Donnybrook, Antelope, Oregon
Description: Thick rounded back with polished face. Brown and dull yellow outer chambered area with a transparent blue on inner area, and a chalky white hollowed-out center.
PHYSICAL CHARACTERISTICS:
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.
Fracture: Conchoidal
Hardness: 7 Quartz
Luster: Waxy
Rock Type: Sedimentary
Specific Gravity: 2.58-2.64
Streak: WhiteCollection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationDimensions
Width
4-1/2 inDepth
2 inLength
6-1/4 inLocation
Location
Rolling Display
RD-12Room
Mentzer HallBuilding
Crater Rock MuseumCategory
PermanentDate
September 30, 2023
