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The structure of gypsum consists of layers of calcium (Ca 2+) and sulfate (SO 2− 4) ions tightly bound together. These layers are bonded by sheets of anion water molecules via weaker hydrogen bonding, which gives the crystal perfect cleavage along the sheets (in the {010} plane). [4] [14]
Selenite, satin spar, desert rose, and gypsum flower are crystal habit varieties of the mineral gypsum.. All varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate (meaning that it has two molecules of water), with the chemical formula CaSO 4 ·2H 2 O. Selenite contains no significant selenium – The similar names both derive from Greek selḗnē ...
The compound exists in three levels of hydration corresponding to different crystallographic structures and to minerals: CaSO 4 : anhydrous state. [6] The structure is related to that of zirconium orthosilicate (zircon): Ca 2+ is 8-coordinate, SO 2− 4 is tetrahedral, O is 3-coordinate. CaSO 4 ·2H 2 O (gypsum and selenite (mineral ...
Crystal structure of anhydrite. Anhydrite is most frequently found in evaporite deposits with gypsum; it was, for instance, first discovered in 1794 in a salt mine near Hall in Tirol. In this occurrence, depth is critical since nearer the surface anhydrite has been altered to gypsum by absorption of circulating ground water.
The ambient sand that is incorporated into the crystal structure, or otherwise encrusts the crystals, varies with the local environment. If iron oxides are present, the rosettes take on a rusty tone. The desert rose may also be known by the names: sand rose, Sahara rose, rose rock, selenite rose, gypsum rose and baryte (barite) rose.
Cone-in-cone structures in limestone. Cone-in-cone structures in limestone. Cone-in-cone structures are secondary sedimentary structures that form in association with deeper burial and diagenesis. They consist of concentric inter-bedded cones of calcite or more rarely gypsum, siderite or pyrite.
Ulexite collected from the Flat Bay gypsum quarry in Newfoundland exhibits acicular "cotton balls" of crystals with a nearly square cross-section formed by the equal development of two pinacoids. The crystals are about 1–3 μm thick and 50–80 μm long, arranged in loosely packed, randomly oriented overlapping bundles (Papezik and Fong, 1975 ...
Aragonite crystals are contrasted with those made of calcite (another variety of calcium carbonate) in that the latter tend to be stubby or dog-tooth-like ("rhombohedral", rather than acicular). Anthodites often have a solid core of aragonite and may have huntite or hydromagnesite deposited near the ends of the branches.