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January 14, 2018 Weekly Geology Guest, Gypsum

January 13, 2018
Greetings from the Bluff Park Back Porch, way up yonder on Shades Mountain (1,109′) in Alabama:
 
 
This week’s industrial mineral is Gypsum.
 

 

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O.[3]
It is widely mined and is used as a fertilizer, and as the main constituent in many forms of plaster, blackboard chalk and wallboard.
A massive fine-grained white or lightly tinted variety of gypsum, called alabaster, has been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, the Byzantine Empire and the Nottingham alabasters of Medieval England.
Mohs scale of mineral hardness, based on scratch hardness comparison, defines hardness value 2 as gypsum.
It forms as an evaporite mineral and as a hydration product of anhydrite.

Crystal varieties

Main article: Selenite (mineral)
Gypsum occurs in nature as flattened and often twinned crystals, and transparent, cleavable masses called selenite.
Selenite may also occur in a silky, fibrous form, in which case it is commonly called “satin spar”. Finally, it may also be granular or quite compact. In hand-sized samples, it can be anywhere from transparent to opaque. A very fine-grained white or lightly tinted variety of gypsum, called alabaster, is prized for ornamental work of various sorts. In arid areas, gypsum can occur in a flower-like form, typically opaque, with embedded sand grains called desert rose. It also forms some of the largest crystals found in nature, up to 12 m (39 ft) long, in the form of selenite.https://en.wikipedia.org/wiki/Gypsum#cite_note-8

1.  Uplighter lamp, white and brown Italian alabaster, base diameter 13 cm (20th century)

Lamp made from Italian alabaster. The base is 5 inches (13 cm) in diameter. Taken in England by Adrian Pingstone in May 2003 and released to the public domain.

2.    Gypsum crystals in the Cave of the Crystals in Mexico. Note person for scale

Alexander Van DriesscheGaianauta received this from Alexander Van Driessche via Email.
Gypsum crystals of the Naica cave. Note person for scale. Author: Alexander Van Driessche

3.    Veins of gypsum in Caprock Canyons State Park, Texas

Fredlyfish4Own work
Gypsum layers in a wash that have been exposed by erosion in Caprock Canyons State Park, Texas.

4.Golden gypsum crystals from Winnipeg

Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
Gypsum (Var.: Gypsum) Locality: Red River Floodway, Winnipeg, Manitoba, Canada (Locality at mindat.org) On a recent trip to Winnipeg, we picked up 10 very unusual specimens of different sorts from the guy who mines them in the clay of the Red River Floodway. This one has the familiar ball shape, but instead of the normally golden-sherry color, the crystals are gem-clear. A single sharp, gemmy crystal rises in one place to crown the specimen. 4 x 2.8 x 2.8 cm

5.    Unusual selenite gypsum from the Red River, Winnipeg, Manitoba, Canada

Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
Gypsum (Var.: Gypsum) Locality: Red River Floodway, Winnipeg, Manitoba, Canada (Locality at mindat.org) Size: 5.2 x 3.4 x 2.9 cm. These strange floater balls of gypsum crystals formed deep in clay beds in the floodway of the Red River, and have been mined there (with a lot of labor) since the 60s. They are truly beautiful, particularly when you have just one or two twinned crystals rising from the rest of the ball in isolation, as here.

6.    Gypsum sand from White Sands National Monument, New Mexico

Wilson44691Own work
Wilson44691Own work
Gypsum sand from White Sands National Monument, New Mexico. Photograph by Mark A. Wilson (Department of Geology, The College of Wooster).

7.    Green gypsum crystals from Pernatty Lagoon, Mt Gunson, South Australia – its green color is due to presence of copper ions.

Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
Gypsum (Var.: Gypsum) Locality: Pernatty Lagoon, Mt Gunson, Stuart Shelf area, Andamooka Ranges – Lake Torrens area, South Australia, Australia (Locality at mindat.org) Okay, this specimen was very difficult to shoot, so PLEASE NOTE that the interior crystals are NOT deep green but actually the lighter green of the smaller photo. What a beautiful specimen this is, an intact pocket of rounded crystal blooms! The back was sawn flat to cut this pocket out of the matrix of massive gypsum. 9.4 x 7.2 x 3.9 cm

8.    Desert roses (Gypsum) Locality : Southern Tunisia Size : 47 × 33 cm.

Didier DescouensOwn work

9.    gypsum var. selenite : Santa Eulalia District, Mun. de Aquiles Serdán, Chihuahua, Mexico

Gypse-sélénite 3.jpeg
Parent GéryOwn work
 
 
 

10.    Gypsum flowers, Bou Azer East deposit, Bou Azer District, Tazenakht, Ouarzazate Province, Souss-Massa-Draâ Region, Morocco

Parent GéryOwn work
gypsum var. selenite, ankerite : Bou Azer East deposit, Bou Azer, Bou Azer District (Bou Azzer District), Tazenakht, Ouarzazate Province, Souss-Massa-Draâ Region, Morocco
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Editors Note:  It is the intent of this site to keep this discussion as simple as possible, so as to educate the interested general public and not to discuss with the geology crowd the latest geologic theories and nuances.  Thanks, R
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“No copyright infringement intended.
The rights belong to their respective owners”

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We will now continue down the Industrial Mineral dusty trail and continue with Halite.
 
Enjoy the adventure!
 
Thanks,
 

 

R
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