Name/Title
Quartz var.ObsidianEntry/Object ID
78.59.986Description
Chemical Composition: SiO2
Crystal System: Triclinic System
Description: Common Name: Obsidian
Chemistry: SiO2 , Silicon dioxide
Class: Class: Silicates
Location: Glass Mtn, Eastern OR
Description: (Delmar) Obsidian [volcanic glass] from a double flow. Polished side shows clear division between halves; one in black with some swirled orange and 'floating' white specks, the other in swirled orange with some black and a sheen resembling Tigereye.
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: Glassy
Occurrence: Quartz is an essential constituent of granite and other felsic igneous rocks. It is very common in sedimentary rocks such as sandstone and shale and is also present in variable amounts as an accessory mineral in most carbonate rocks. It is also a common constituent of schist, gneiss, quartzite and other metamorphic rocks. Because of its resistance to weathering it is very common in stream sediments and in residual soils.
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.
Specific Gravity: 2.65
Streak: white
Variety: Quartz is the most common mineral on the face of the Earth. It is found in nearly every geological environment and is at least a component of almost every rock type. It frequently is the primary mineral, >98%. It is also the most varied in terms of varieties, colors and forms. This variety comes about because of the abundance and widespread distribution of quartz. A collector could easily have hundreds of quartz specimens and not have two that are the same due to the many broad catagories.Collection
Delmar Smith Mineral CollectionDimensions
Width
4-3/4 inLength
6-3/4 inDimension Notes
Dimension taken at widest pointsLocation
Location
Container
Front RowDrawer
BottomShelf
Left, LeftBuilding
Founders RoomCategory
PermanentMoved By
Ray BlohmDate
January 4, 2012Location
Container
Front RowDrawer
BottomShelf
Left, LeftWall
WestBuilding
Founders RoomCategory
PermanentMoved By
Ray BlohmDate
January 4, 2012Location
Shelf
LeftCabinet
Case # 5Room
Mentzer HallBuilding
Crater Rock MuseumCategory
Permanent
