Smoky Quartz

Object/Artifact

-

Crater Rock Museum

Name/Title

Smoky Quartz

Entry/Object ID

2013.1.3

Description

Chemical Composition: SiO2 Crystal System: Monoclinic System Description: Common Name: Quartz (Smokey) Chemistry: SiO2 Group: Silicates Location: Minas Gerais, Brazil Description: This is a tall, transparent crystal with very distinct rough patterns within. Physical Description: •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. •Notable Occurrences of amethyst are Brazil, Uraguay, Mexico, Russia, Thunder Bay area of Canada, and some locallities in the USA. For Smoky Quartz; Brazil, Colorado, Scotland, Swiss Alps among many others. Rose Quartz is also wide spread but large quantities come from brazil as do the only large find of Rose Quartz prisms. Natural citrine is found with many amethyst deposits but in very rare quantities. Fine examples of Rock crystal come from Brazil (again), Arkansas, many localities in Africa, etc. Fine Agates are found in, of course, Brazil, Lake Superior region, Montana, Mexico and Germany. •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 Rock Type: Sedimentary Specific Gravity: 2.65 Streak: White Variety: •Agate is a banded variety (sometimes with translucent bands) •Bloodstone is green with red speckles •Carnelian is yellow to orange •Chrysoprase is green •Flint is generally black with a fibrous microscopic structure •Jasper is any colorful agate •Onyx is black, white, or alternating black and white •Sard is yellow to brown •Sardonyx is banded, alternating sard and (usually white) onyx

Collection

RAGM Mineral Collection

Dimensions

Height

7-1/2 in

Width

2 in

Length

2-3/4 in

Location

Location

Display Case

FS-3

Room

Frieda Smith Hall

Building

Crater Rock Museum

Category

Permanent

Date

August 18, 2023