Name/Title
Calcite / SphaleriteEntry/Object ID
2009.62.88Description
Chemical Composition: see description
Crystal System: Tetragonal System
Description: Common Name: Calcite / Sphalerite
Chemistry: CaCO3, Calcium Carbonate / (Zn, Fe)S, Zinc Iron Sulfide
Group: Carbonates / Sulfides
Location: Carthage, Tennessee
Description: Large calcite crystal translucent white turning to shades of brown at the pointed end. There are two sphalerite crystals, black in color jutting from both sides of the calcite crystal at its base
PHYSICAL CHARACTERISTICS OF CALCITE:
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.
PHYSICAL CHARACTERISTICS OF SPHALERITE:
Color is typically black but can be brown, yellow, reddish, green, and less commonly white or colorless.
Luster is adamantine or resinous or submetallic to earthy in massive forms.
Transparency crystals are transparent to translucent.
Crystal System is isometric; bar 4 3m
Crystal Habits can be complicated with the rhombic dodecahedron, tetrahedron and combinations of these having cubic and tristetrahedron faces giving the crystals multiple faces of often indistinct forms. To add more confusion to the indistinct crystals, twinning is common and sometimes pervasive. Massive forms are common and can be granular, earthy, botryoidal, concretionary and fibrous. An aggregate of botryoidal crusts with layers of wurtzite and galena is called "Schalenblende" is sometimes cut and polished as an ornamental stone.
Cleavage is perfect in six directions forming dodecahedrons.
Fracture is conchoidal, but rarely seen because of frequent cleavage.
Hardness is 3.5-4
Specific Gravity is approximately 4.0 (heavier than average, but light when compared to most metallic minerals)
Streak is yellow to light brown (unusually light colored for a normally dark mineral).
Other Characteristics: Striations on tetrahedral faces, triboluminescent (meaning it may glow if crushed), an index of refraction of 2.37 - 2.42, a dispersion (fire) of 0.156 and finally sphalerite is pyroelectric (meaning that it forms a slight electrical charge when heated or cooled).
Associated Minerals almost always include galena, pyrite, fluorite, chalcopyrite, quartz, calcite, magnetite, pyrrhotite and many others.
Best Field Indicators are crystal habits, streak, cleavage, high luster, softness and twinning.
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.
Shpalerite forms in sulfide ore veins in all rock classes.
Specific Gravity: 2.7
Streak: white
Variety: It is one of the most common minerals on the face of the Earth, comprising about 4% by weight of the Earth's crust and is formed in many different geological environments. Calcite can form rocks of considerable mass and constitutes a significant part of all three major rock classification types. It forms oolitic, fossiliferous and massive limestones in sedimentary environments and even serves as the cements for many sandstones and shales. Limestone becomes marble from the heat and pressure of metamorphic events. Calcite is even a major component in the igneous rock called carbonatite and forms the major portion of many hydrothermal veins.
With calcite so abundant and so widely distributed it is no wonder that it can be so varied. The crystals of calcite can form literally a thousand different shapes by combining the basic forms of the positive rhombohedron, negative rhombohedron, steeply, moderately and slightly inclined rhombohedrons, various scalahedrons, prism and pinacoid to name a few of the more common forms. There are more than 300 crystal forms identified in calcite and these forms can combine to produce the thousand different crystal variations. Calcite also produces many twin varieties that are favorites among twin collectors. There are also phantoms, included crystals, color varieties, pseudomorphs and unique associations. There simply is no end to the varieties of calcite.
Sphalerite is one of the very few minerals that has a total of six directions of cleavage. If all of them were to be perfectly cleaved on a single crystal it would form a rhombic dodecahedron. Identifying all six directions in a single cleaved crystal is quite difficult due to the multiple twinning and the many directions. Only the fact that there is abundant cleavage at different directions can easily be seen in most cleaved specimens.
Sphalerite can be difficult to identify because of its variable luster, color, abundant but obscured cleavage and crystal habits. So difficult was sphalerite for miners to distinguish from more valuable minerals such as galena, acanthite and tetrahedrite, that they named it sphalerite which is Greek for treacherous rock and blende is German for blind or deceiving.Collection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationDimensions
Width
11 inDepth
2 inLength
10 inWeight
18.96 ozDimension Notes
Dimension taken at widest pointsLocation
Location
Container
CenterDrawer
3rd ShelfShelf
left, leftWall
South wallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Steve MillerDate
January 16, 2010Location
Drawer
far leftShelf
left side top shelf, left side top shelfWall
south wallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
scottDate
September 19, 2009Location
Drawer
3rd from leftShelf
left side middle she, left side middle sheWall
south wallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
scottDate
September 19, 2009Location
Drawer
3rd from leftShelf
left side middle she, left side middle sheWall
south wallRoom
Delmar SmithBuilding
left side middle 3rd rock from left/left side middle 3rd roCategory
PermanentMoved By
scottDate
September 19, 2009Location
Drawer
3rd from leftShelf
left side middle she, left side middle sheWall
south wallRoom
Delmar SmithBuilding
left side middle 3rd rock from leftCategory
PermanentMoved By
scottDate
September 19, 2009Location
Drawer
3rd from leftShelf
left middle shelf, left middle shelfWall
south wallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
scottDate
September 19, 2009Location
Container
Right / BackDrawer
BottomShelf
RightCabinet
Case #32Wall
EastBuilding
Freida Smith HallCategory
Permanent