Gypsum is a soft sulfate
mineral composed of calcium sulfate
dihydrate, with the chemical formula
CaSO4·2H2O. 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.
Selenite, satin spar, desert
rose, and gypsum flower are four
varieties of the mineral gypsum; all
four varieties show obvious crystalline
structure. The four "crystalline"
varieties of gypsum are sometimes
grouped together and called selenite.
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 CaSO4·2H2O. Selenite
contains no significant selenium; the
similarity of names comes from both
substances being named from the Ancient
Greek word for the Moon.
Some of the largest crystals ever found
are selenite crystals - the largest
specimen found in the Naica Mine's Cave
of the Crystals is 12 metres long and
weighs 55 tons.
Cave of the Crystals
Cave of the Crystals or Giant Crystal
Cave (Spanish: Cueva de los Cristales)
is a cave connected to the Naica Mine at
a depth of 300 metres (980 ft), in
Naica, Chihuahua, Mexico.
The main chamber contains giant selenite
crystals (gypsum, CaSO4·2 H2O), some of
the largest natural crystals ever found.
The cave's largest crystal found to date
is 12 m (39 ft) in length, 4 m (13 ft)
in diameter and 55 tons in weight. The
cave is extremely hot, with air
temperatures reaching up to 58 °C (136
°F) with 90 to 99 percent humidity. The
cave is relatively unexplored due to
these factors. Without proper
protection, people can only endure
approximately ten minutes of exposure at
The cave was discovered by the brothers
Eloy and Javier Delgado. A group of
scientists known as the Naica Project
have been heavily involved in
researching these caverns.