Gypsum

Gypsum is a very soft mineral (hardness: 2 on Mohs Scale)

It’s most important identifying characteristic is it’s softness. If you are unable to easily scratch it with a fingernail, then it is likely you have a different mineral. Also because gypsum has natural insulating properties, it feels warmer to the touch than other rocks.

Alabaster is a massive form of gypsum, meaning that its crystals are not obvious to the naked eye.

Selenite is the crystal form of the mineral gypsum, it is often transparent and colorless.

If selenite crystals show translucency, opacity, and/or color, it is caused by the presence of other minerals.

Gypsum is formed as an evaporative mineral, frequently found in alkaline lake muds, clay beds, evaporated seas, salt flats, and caves. Gypsum, also, is frequently found in conjunction with other minerals. Gypsum formations have been dated to almost every geologic age.

 

For more information about Gypsum try these links:

http://www.minerals.net/mineral/gypsum.aspx

http://geology.com/minerals/gypsum.shtml

http://www.mindat.org/min-1784.html