Name/Title
Aurichalcite / AragoniteEntry/Object ID
2009.62.87Description
Chemical Composition: see description
Crystal System: Orthorhombic System
Description: Common Name: Aurichalcite / Aragonite
Chemistry: (Zn, Cu)5(CO3)2(OH)6, Zinc Copper Carbonate Hydroxide / CaCO3, Calcium Carbonate
Group: Carbonates
Location: Santa Eulalia, Chihuahua, Mexico
Description: Specimen has a druzy white crystalline structure nodular in shape with an area of small needle-like crystals turquoise in color.
PHYSICAL CHARACTERISTICS OF AURICHALCITE:
Color is usually a grass green but varies from white to green to greenish blue to light blue.
Luster is silky to fibrous or pearly on more massive specimens.
Transparency crystals are transparent to translucent.
Crystal System is orthorhombic; 2 2 2
Crystal Habits include radiating tufts of acicular crystals. also encrustations of fiberous or lamellar masses.
Hardness is 1 - 2
Specific Gravity is 3.6 - 4 (above average for non-metallic minerals)
Cleavage is perfect in one direction.
Fracture is uneven or fiberous.
Streak is white to pale shades that depend on color.
Associated Minerals include limonite, smithsonite, azurite, malachite, rosasite and calcite.
Other Characteristics: effervesceses easily in cold dilute hydrochloric acid.
Best Field Indicators are crystal habits, color, associations, softness and reaction to acid.
PHYSICAL CHARACTERISTICS OF ARAGONITE:
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: conchoidal
Hardness: 2 Gypsum
Luster: Vitreous
Occurrence: Aurichalcite is a carbonate mineral, usually found as a secondary mineral in copper and zinc deposits Aurichalcite forms in the oxidation zones of zinc-copper deposits.
The environments for the formation of aragonite include hot springs deposits, cavities in volcanic rocks, caves and mines.
Specific Gravity: 3.6-4.0
Streak: white
Variety: Aurichalcite forms in the oxidation zones of zinc-copper deposits. Crystals are acicular or fibrous and found in tufted aggregates. The color is an attractive grass green to pale green. Aurichalcite will at times partially cover red limonite and be associated with such colorful minerals as azurite, smithsonite and malachite. Specimens of aurichalcite certainly make for colorful "landscape" specimens.
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
Height
3-1/2 inWidth
3 inLength
6 inWeight
2.33 ozDimension Notes
Dimension taken at widest pointsLocation
Location
Display Case
FS-4-ARoom
Frieda Smith HallBuilding
Crater Rock MuseumDate
January 4, 2024Location
Container
RightDrawer
3rd shelfShelf
Left, LeftWall
East WallBuilding
Freida Smith HallCategory
PermanentMoved By
Steve MillerDate
June 29, 2012Location
Container
CenterDrawer
3rd ShelfShelf
left, leftWall
South wallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Steve MillerDate
January 16, 2010Location
* Untyped Location
Needs Updated Location - 2022Category
PermanentMoved By
Scott LonganDate
September 19, 2009Location
Container
RightDrawer
3rd shelfShelf
LeftCabinet
Case #60Wall
East WallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
Permanent