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CALCIUM SULFATES (GYPSUM)

SATIN SPAR

Satin Spar (gypsum)
Origin Morocco
Size  
Cost $40.00
Acquired March, 1997
Where East Windsor, CT (show)
Hardness 2
SG 2.32
Streak white
Chemistry CaSO4.2H2O
GYPSUM is the most common SULFATE MINERAL. A hydrated calcium sulfate, it serves as a raw material in plaster of Paris and is also used as fertilizer.

Crystals are tabular, and diamond-shaped. Twinning is common. The mineral has perfect cleavage in one direction. It varies from colorless to white, gray, greensih, yellowish, brownish, and reddish. It is transparent to opaque, with a vitreous luster (pearly on cleavages); fibrous forms may be silky, massive forms are often dull.

Rosette-shapped masses are called DESERT ROSE, and radiating forms are termed daisy gypsum. Alabaster is a massive, fine-grained form. SATIN SPAR, a fibrous form with a silky luster. Both alabaster and satin spar are employed as ornamental stone. A transparent, colorless variety called SELENITE is used as optical material.

Gypsum occurs with halite and other evaporite minerals in thick, extensive beds that were deposited from seas or playa lakes. Such beds often alternate with limestone and shale. It also forms by the alteration of ANHYDRITE and in other ways. Gypsum is found extensively in many areas of the world.
Gypsum
Origin _
Size _
Cost $211.00
Acquired June, 1998
Where Banff, AB, Canada

GOLDEN SELENITE

Golden Selenite
Origin Cerrode-Pasco, Peru
Size  
Cost $22.50
Acquired October, 2002
Where N Conway, NY (shop)

SELENITE

Selenite
Origin Lake Gilles, Australia
Size  
Cost $40.00
Acquired March, 2000
Where Manchester, CT

FISHTAIL SELENITE

Fishtail Selenite
Origin  
Size  
Cost $25.00
Acquired October, 1997
Where Burlington, CT

SELENITE

Selenite
Origin 
Size427 grams
Cost $35.00
Acquired May, 1994
WhereMoab, UT

SELENITE

Mica
Origin Mt. Mica, Spokane, WA
Size  
Cost $9
Acquired July, 2013
Where Spokane, WA (shop)
Labelled as "mica" by the Spokane rock shop from which it was purchased, this piece more closely resembles selenite samples acquired from various parts of the world than mica.

SELENITE/GYPSUM

Origin
Size  
Cost
Acquired June, 2003
Where New Brunswick (shop)

SELENITE/GYPSUM

_
Origin  
Size  
Cost
Acquired  
Where  

SAND ROSE

sand rose
Origin  
Size  
Cost $50
Acquired May, 2005
Where Jessieville, AR (shop)

DESERT ROSE

Selenite
Origin 
Size698 grams
CostGift from Mom & Dad
Acquired 
DESERT ROSE is the colloquial name given to rose-like formations of crystal clusters of gypsum or baryte which include abundant sand grains. The 'petals' are crystals flattened on the c crystallographic axis, fanning open in radiating flattened crystal clusters.

The rosette crystal habit tends to occur when the crystals form in arid sandy conditions, such as the evaporation of a shallow salt basin. The crystals form a circular array of flat plates, giving the rock a shape similar to a rose blossom. Gypsum roses usually have better defined, sharper edges than baryte roses. Celestine and other bladed evaporite minerals may also form rosette clusters. They can appear either as a single rose-like bloom or as clusters of blooms, with most sizes ranging from pea sized to 4 inches (10 cm) in diameter.

The ambient sand that is incorporated into the crystal structure, or otherwise coats the crystals with encrustations, varies with the local environment. If iron oxides are present, the rosettes take on a rustic tone.

The desert rose may also be known by the names:SAND ROSE, rose rock, selenite rose, gypsum rose and baryte (barite) rose. [http://en.wikipedia.org/wiki/Desert_rose_(crystal)]

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updated 08/13/14