Periclase is sometimes used as a gemstone although it lacks good hardness
and is generally limited in colors. Periclase is isostructural with
NaCl, which has simple cubic packing and produces cubic and octahedral
Periclase is relatively scarce and is found in marbles being
formed from the dissolution of dolomite,
CaMg(CO3)2 , into MgO-periclase,
and CO2-carbon dioxide. This dissolution takes
place during metamorphism. If the periclase rich marbles are exposed to
weathering the periclase easily alters to either brucite,
Mg(OH)2 or hydromagnesite,
The yellow brown and black colors of
periclase are due to the presence of iron. Specimens of periclase can be
very attractive as brightly lustered, smoothly faceted crystals projecting
out of the otherwise formless rough marble host rock.
Color is colorless, white, gray, yellow to brown or black
Luster is vitreous to adamantine.
Transparency crystals are transparent to translucent.
Crystal System is isometric; 4/m bar 3 2/m
Crystal Habits include the typical cubes and octahedrons as
well as rounded indistinct grains.
Cleavage is perfect in three directions forming cubes.
Hardness is 5.5
Specific Gravity is 3.6 (slightly above average)
Streak is white.
Other Characteristics: Crystals may dull in humid air.
Associated Minerals include
Notable Occurrences include Monte Somma, Vesuvius, Italy; Crestmore,
California, USA and Nordmark, Varmland, Sweden.
Best Field Indicators are crystal habit, luster, hardness, cleavage,
associations and localities.