Name/Title
CalciteEntry/Object ID
2004.1.143Description
Chemical Composition: CaCO3
Crystal System: Triclinic System
Description: Common Name: Calcite
Group Name: Calcite
Chemistry: CaCO3
Location: Challenger Cave, Nuevo Leon, Mexico
Description: Large, rhomb with a translucent pink to orange color.
PHYSICAL CHARACTERISTICS:
Color is extremely variable but generally white or colorless or with light shades of yellow, orange, blue, pink, red, brown, green, black and gray. Occasionally iridescent.
Luster is vitreous to resinous to dull in massive forms.
Transparency: Crystals are transparent to translucent.
Crystal System is trigonal; bar 3 2/m
Crystal Habits are extremely variable with almost any trigonal form possible. Common among calcite crystals are the scalenohedron, rhombohedron, hexagonal prism, and pinacoid. Combinations of these and over three hundred other forms can make a multitude of crystal shapes, but always trigonal or pseudo-hexagonal. Twinning is often seen and results in crystals with blocky chevrons, right angled prisms, heart shapes or dipyramidal shapes. A notch in the middle of a doubly terminated scalenohedron is a sure sign of a twinned crystal. lamellar twinning also seen resulting in striated cleavage surfaces. Pseudomorphs after many minerals are known, but easily identified as calcite. Also massive, fibrous, concretionary, stalactitic, nodular, oolitic, stellate, dendritic, granular, layered, etc. etc.
Cleavage is perfect in three directions, forming rhombohedrons.
Fracture is conchoidal.
Hardness is 3 (only on the basal pinacoidal faces, calcite has a hardness of less than 2.5 and can be scratched by a fingernail).
Specific Gravity is approximately 2.7 (average)
Streak is white.
Other Characteristics: refractive indices of 1.49 and 1.66 causing a significant double refraction effect (when a clear crystal is placed on a single line, two lines can then be observed), effervesces easily with dilute acids and may be fluorescent, phosphorescent, thermoluminescence and triboluminescent.
Associated Minerals are numerous but include these classic associations: Fluorite, quartz, barite, sphalerite, galena, celestite, sulfur, gold, copper, emerald, apatite, biotite, zeolites, several metal sulfides, other carbonates and borates and many other minerals.
Best Field Indicators are crystal habit, reaction to acid, abundance, hardness, double refraction and especially cleavage.
Fracture: Conchoidal
Hardness: 3 Calcite
Luster: Vitreous
Occurrence: Notable Occurrences include Pugh Quarry, Ohio; Rosiclare, Illinois; Franklin, New Jersey; Elmwood, Tennessee; Brush Creek and other Missouri, Wisconsin, Kansas and Oklahoma localities, USA; Andreasburg, Harz Mountains and Saxony, Germany; Brazil; Guanajuato, Mexico; Cornwall, Durham and Lancashire, England; Bombay area of India; Eskifjord, Iceland; many African localities as well as others around the world with their own unique varieties.
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.
Specific Gravity: 2.7
Streak: white
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
Suomynona Mineral Collection, Suomynona CollectionAcquisition
Accession
2004.1Source or Donor
Suomynona Mineral CollectionAcquisition Method
DonationDimensions
Width
5 inDepth
6 inLength
7 inDimension Notes
Dimension taken at widest pointsLocation
Location
Display Case
FS-6-ARoom
Frieda Smith HallBuilding
Crater Rock MuseumDate
January 3, 2024Location
Room
Neil JohnsonBuilding
Attic StorageCategory
PermanentMoved By
Lehman R.Date
August 28, 2009Location
Drawer
LeftShelf
Bottom, BottomWall
NorthBuilding
Founders RoomCategory
PermanentMoved By
Lehman R.Date
August 28, 2009Location
Drawer
LeftShelf
Bottom, BottomWall
EastBuilding
Freida HallCategory
PermanentMoved By
Lehman R.Date
August 28, 2009Location
Cabinet
Case #29Wall
EastBuilding
Freida HallCategory
Permanent
