Name/Title
AragoniteEntry/Object ID
2009.62.96Description
Chemical Composition: CaCO3
Crystal System: Orthorhombic System
Description: Common Name: Aragonite
Chemistry: CaCO3, Calcium Carbonate
Group: Carbonates
Location: (Salsigne) Aude, France
Description: White coral-like branching crystals turning a light tan on the leading edges.
PHYSICAL CHARACTERISTICS:
Color can be white or colorless or with usually subdued shades of red, yellow, orange, brown, green and even blue.
Luster is vitreous to dull.
Transparency: Crystals are transparent to translucent.
Crystal System is orthorhombic; 2/m 2/m 2/m
Crystal Habits include twinned hexagonal prismatic crystals as well as a diverse assortment of thin elongated prismatic, curved bladed, steep pyramidal (spiked) and chisel shaped crystals. A branching tree, coral or worm-like delicate form is called "flos ferri". Can also be compact, granular, radially fibrous and massive. Its massive forms can be layered, coralloid, pisolitic, oolitic, globular, stalachtitic and encrusting. Aragonite is a constituent of many species' shell structures. A layered sedimentary marble like formation is called Mexican Onyx and is used for carvings and ornamental purposes. Calcite pseudomorphs of aragonite crystals and formations are common.
Cleavage is distinct in one direction (pinacoidal).
Fracture is subconchoidal.
Hardness is 3.5-4
Specific Gravity is 2.9+ (average for non-metallic minerals)
Streak is white.
Other Characteristics: aragonite effervesces easily in cold dilute hydrochloric acid, is strongly birefringent, is fluorescent and its refractive index is 1.7 .
Associated Minerals include gypsum, barite, smithsonite, malachite, calcite, serpentine, sulfur, celestite, zeolites, quartz, clays, dolomite, limonite, chalcopyrite and wulfenite among many others.
Best Field Indicators are crystal habits, single plane of cleavage and reaction to acid.
Fracture: Subconchoidal
Hardness: 3 Calcite
Luster: Vitreous
Occurrence: The environments for the formation of aragonite include hot springs deposits, cavities in volcanic rocks, caves and mines.
Specific Gravity: 3.5
Streak: white
Variety: Aragonite is a common carbonate mineral and is a polymorph of calcite, which means that it has the same chemistry as calcite but it has a different structure, and more importantly, different symmetry and crystal shapes. Aragonite's more compact structure is composed of triangular carbonate ion groups (CO3), with a carbon at the center of the triangle and the three oxygens at each corner. Aragonite is technically unstable at normal surface temperatures and pressures. It is stable at higher pressures, but not at higher temperatures such that in order to keep aragonite stable with increasing temperature, the pressure must also increase. If aragonite is heated to 400 degrees C, it will spontaneously convert to calcite if the pressure is not also increased. Since calcite is the more stable mineral, why does aragonite even form? Well under certain conditions of formation, the crystallization of calcite is somehow discouraged and aragonite will form instead. After burial, given enough time, the aragonite will almost certainly alter to calcite.Collection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationDimensions
Width
4 inDepth
2-1/2 inLength
4-1/2 inWeight
0.46 ozDimension Notes
Dimension taken at widest pointsLocation
Location
Container
LeftDrawer
BottomShelf
Right, RightWall
EastBuilding
Freida Smith HallCategory
PermanentMoved By
Steve MillerDate
August 15, 2012Location
Container
RightDrawer
2nd ShelfShelf
Center, CenterWall
South wallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Steve MillerDate
January 22, 2010Location
* Untyped Location
Needs Updated Location - 2022Category
PermanentMoved By
Jacob RierDate
September 25, 2009Location
Cabinet
Case #56Wall
CenterBuilding
Freida Smith HallCategory
Permanent