Gypsum
CaSO₄ · 2H₂O

     The occurrence of gypsum at MSH is rare.

PHYSICAL CHARACTERISTICS:

Color is usually colorless or white.
Luster is vitreous; silky on cleavages.
Diaphaneity is transparent.
Crystal System is monoclinic; C2/c.
Crystal Habits include sharp, thin elongated prisms and blades
   to 5mm and drusy microcrystals.
Cleavage {010} is perfect, {100} and {011} are distinct.
Fracture is splintery.
Hardness is 2.
Specific Gravity is approximately 2.3 g/cm³.
Streak is white.
Associated Minerals include mica group and natrolite.
Distinguishing Features: Crystal habit and color.
Origin: Known from antiquity, its name come from the Greek
   gypsos, plaster, alluding to its principal use.

CLASSIFICATION:

REFERENCES:
MinRec 21:325 (1990), Dana 8:598-601 (1997)

DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE:

Legend

Gypsum crystals
© Modris Baum