Name/Title
Arsenic / RealgarEntry/Object ID
78.63.415Description
Chemical Composition: CaCO3,
Crystal System: Triclinic System
Description: Common Name: Arsenic Sulfide / Realgar
Group Name: Sulfides
Chemistry: AsS, Arsenic Sulfide
Location: Mexico
Description: Delmar described this specimen as one, "Realgar or Arsenic Sulfide crystals, orange-red on dark grey matrix rock. It is an iron type and it's what they make arseniic out of.
PHYSICAL CHARACTERISTICS:
•Color is orange to red.
•Luster is resinous, adamantine to sub-metallic.
•Transparency: Crystals are translucent to transparent.
•Crystal System: Monoclinic; 2/m.
•Crystal Habits: include prismatic striated crystals with a rounded diamond-like cross-section. They are terminated by a wedge-like dome. Also found as grains, crusts and earthy masses.
•Cleavage is good in one direction.
•Fracture is subconchoidal.
•Hardness is 1.5 - 2
•Specific Gravity is 3.5 - 3.6
•Streak is orange to orange-yellow.
•Other Characteristics: Realgar is unstable in light; specimens should be stored in complete darkness, rarely some specimens fluoresce under UV light and crystals are pleochroic between dark red and orange red.
•Associated Minerals almost always include orpiment, also calcite, stibnite and other metal sulfide ores.
•Notable Occurrences include most importantly Hunan Province, China; but also Switzerland; Japan; Macedonia; Mercur, Utah, USA; Romania and many other localities.
•Best Field Indicators are of course color as well as crystal habit, association with orpiment, softness and luster.
Fracture: conchoidal
Hardness: 3 Calcite
Luster: Vitreous
Occurrence: Calcite is a common constituent of sedimentary rocks, limestone in particular, much of which is formed from the shells of dead marine organisms. Approximately 10% of sedimentary rock is limestone.
Calcite is the primary mineral in metamorphic marble. It also occurs as a vein mineral in deposits from hot springs, and it occurs in caverns as stalactites and stalagmites.
Calcite may also be found in volcanic or mantle-derived rocks such as carbonatites, kimberlites, or rarely in peridotites. Lublinite is a fibrous, efflorescent form of calcite.[8]
Calcite is often the primary constituent of the shells of marine organisms, e.g., plankton (such as coccoliths and planktic foraminifera), the hard parts of red algae, some sponges, brachiopoda, echinoderms, most bryozoa, and parts of the shells of some bivalves, such as oysters and rudists). Calcite is found in spectacular form in the Snowy River Cave of New Mexico as mentioned above, where microorganisms are credited with natural formations. Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes.
Rock Type: Sedimentary
Specific Gravity: 2.7
Streak: white
Texture: Crystaline to Mircocrystaline
Variety: There are several varieties of calcite and it would be impossible to describe them all. However there are a few standouts. Possibly the most well known of calcite's varieties is its most common form, the classic scalenohedron or "Dogtooth Spar" as it is sometimes called. This variety appears as a double pyramid or dipyramid, but is actually a distinctly different form. The point of the scalenohedron is sharp and resembles the canine tooth of a dog, hence the name. Beautiful clear colorless or amber-orange examples of this variety are considered classics and outstanding examples come from Pugh Quarry, Ohio; Cornwall, England and Elmwood, Tennessee but the variety is found worldwide.
Not necessarily a variety of calcite, cave formations are certainly a unique aspect of calcite's story. Calcite is the primary mineral component in cave formations. Stalactites and stalagmites, cave veils, cave pearls, "soda straws" and the many other different cave formations that millions of visitors to underground caverns enjoy are made of calcite. It is the fact that calcite is readily dissolved that these formations occur. Overlying limestones or marbles are dissolved away by years and years of slightly acidic ground water to percolate into the caverns below. In fact the caverns themselves may have been the result of water dissolving away the calcite rich rock. As the calcite enriched water enters a relatively dry cavern, the water starts to evaporate and thus precipitate the calcite. The resulting accumulations of calcite are generally extremely pure and are colored if at all, by very small amounts of iron or other impurities.
Mexican onyx is a variety of calcite that is used extensively for ornamental purposes. It is carved into figurines and is so popular that almost every child in the USA owns a small onyx animal or two. Carvings such as vases, bookends, plates, eggs, obilisks, pyramids and statues are all popular. It is not the same onyx as the quartz variety of onyx which is a little more precious (it is used in jewelry) and is banded white and black. To avoid confusion it is best to refer to it as Mexican Onyx. Mexican onyx is banded with multiple orange, yellow, red, tan, brown and white colors that have marble-like texture. The carvings are quite attractive and affordable; a rare combination!
Another variety is the so called "Iceland Spar", which is basically clear cleaved fragments of completely colorless (ice-like) calcite. Originally discovered and named after Eskifjord, Iceland where the calcite is found in basalt cavities. In rock shops around the world, iceland spar is available in large quantities and at affordable prices and are popular among children. Most of today's iceland spar comes from Mexico. The iceland spar displays the classic cleavage form of calcite, the rhombohedron. Iceland spar was and is used for optical equipment and during World War II it was a strategic mineral as it was used for the sighting equipment of bombardiers and gunners. It is iceland spar that best demonstrates the unique property of calcite called double refraction.Collection
Delmar Smith Crystal CollectionAcquisition
Accession
78.63Source or Donor
Delmar Smith Crystal CollectionAcquisition Method
DonationOther Names and Numbers
Other Number
Other Number: 1978.63.474Dimensions
Width
2 inDepth
1-1/4 inLength
4-1/2 inDimension Notes
Dimension taken at widest pointsLocation
Location
Display Case
FS-12Room
Frieda Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Curtis GardnerDate
May 25, 2023Notes
Added current locationLocation
Drawer
2nd ShelfShelf
Left, LeftWall
EastBuilding
Freida Smith HallCategory
PermanentMoved By
Steve MillerDate
August 10, 2012Location
* Untyped Location
Needs Updated Location - 2022Category
PermanentMoved By
Catherine BoydDate
December 26, 2008Location
Drawer
BottomShelf
CenterCabinet
Case# 19Wall
WestBuilding
Freida Smith HallCategory
Permanent