Name/Title
Quartz var. AmethystEntry/Object ID
78.63.342Description
Assemblage Zone: pegmatite dikes
Chemical Composition: SiO2
Crystal System: Triclinic System
Description: Common Name: Amethyst
Group Name: Silciate
Chemistry: SiO2 Silcon dioxide
Location: Unknown
Description: Three individual Amethyst crystals imbedded in white quartz crystal.
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: Amethyst can occur as long prismatic crystals that have a six sided pyramid at either end or can form as druzes that are crystalline crusts that only show the pointed terminations. As a mineral specimen, amethyst is popular for its color and nice crystal shapes that produce a handsome, purple, sparkling cluster.
However, amethyst is not the same everywhere. Different localities can produce a unique amethyst to that particular region or even to that particular mine. Experts can often identify the source mine that a particular amethyst came from. The key to this is the specimen's color, shape of crystal, inclusions, associations and character of formation.
Rock Type: Sedimentary
Specific Gravity: 3.9
Streak: white
Texture: crystaline
Variety: Amethyst is the purple variety of quartz and is a popular gemstone. If it were not for its widespread availability, amethyst would be very expensive. The name "amethyst" comes from the Greek and means "not drunken." This was maybe due to a belief that amethyst would ward off the effects of alcohol, but most likely the Greeks were referring to the almost wine-like color of some stones that they may have encountered. Its color is unparalleled, and even other, more expensive purple gemstones are often compared to its color and beauty. Although it must always be purple to be amethyst, it can and does have a wide range of purple shades.Collection
Delmar Smith Mineral CollectionAcquisition
Accession
78.63Source or Donor
Delmar Smith Crystal CollectionAcquisition Method
DonationDimensions
Width
1-1/2 inDepth
2-1/4 inLength
1-1/2 inDimension Notes
Dimension taken at widest points.
Weight is to heavy to weightLocation
Location
Shelf
CS-E-1Room
Curation StorageBuilding
Crater Rock MuseumCategory
StorageMoved By
CuratorDate
February 23, 2024