THE MINERAL DIOPSIDE

Chemistry: CaMgSi2 O6, Calcium Magnesium Silicate
Class: Silicates
Subclass: Inosilicates
Group: Pyroxenes
Uses: occasionally used as a gemstone and as a mineral specimen.
Specimens

Diopside is an important rock forming mineral in several metamorphic and basic to ultra basic igneous rocks, also found in meteorites. Diopside is a part of an important solid solution series of the pyroxene group. The series includes the minerals hedenbergite, CaFeSi2 O6, and augite, (Ca, Na)(Fe, Mg, Al)(Al, Si)2 O6. A series occurs when ions (in this case iron and magnesium) can freely substitute between each other. Diopside is the magnesium rich end member of the series. The diopside-hedenbergite series is analogous to the amphiobole, tremolite- actinolite series.

Diopside has several varieties, including a chromium-rich gem variety called chrome diopside. Violan is rare blue variety found in some localities in Italy. There is also a green "cat's eye" variety that contains minute inclusions, probably of rutile, that reflect light in such a way as to produce a lively linear luminscence within the crystal. Still another variety is quite dark, with included rutile needles aligned so as to produce a 4-rayed star, hence the name star diopside. Ordinary diopside is typically white or green and can have a nice glassy luster. While the color of chrome diopside is much brighter, many specimens of ordinary diopside are also cut for gemstones. Mineral specimens of diopside can be very striking in appearance, and of interest to mineral collectors.

PHYSICAL CHARACTERISTICS:

Color is clear, white, blue, bright and pale green to yellowish or greenish brown.
Luster is vitreous.
Transparency crystals are transparent to translucent.
Crystal System is monoclinic; 2/m
Crystal Habits include short prismatic, rarely tabular crystals. The square cross section is distinctive in the prismatic crystals. Also compact, granular, columnar and massive.
Cleavage is perfect in two lengthwise directions at close to right angles and a basal parting direction is sometimes seen.
Fracture is uneven, even rough.
Hardness is 5 - 6
Specific Gravity is approximately 3.3 (slightly above average)
Streak is white.
Other Characteristics: Some specimens have been known to fluoresce and some specimens have inclusions that can form "cat's eyes" if polished in cabachon.
Associated Minerals are grossular, andradite, fluorite, dolomite, chlorite, vesuvianite, phlogopite, actinolite, olivine, iron meteorites and calcite.
Notable Occurrences include St. Lawrence Co., New York, USA; Ural Mountains, Russia; Mt. Vesuvius and other locallities in Italy; Austria; Germany; Sri Lanka; Brazil; Mogok, Burma; Madagascar; Kimberly, South Africa and Outokumpu, Finland.
Best Field Indicators are crystal habit, associations, color, fracture and cleavage.