Description: Pyroxenes are a group of dark-colored rock-forming minerals found in igneous and metamorphic rocks throughout the world. They form under conditions of high temperature and/or high pressure.
Chemical Formula: X•Y•Z2•O6, where
X = Ca, Na, Fe++, Mg, Zn, Mn, or Li;
Y= Mg, Fe+++, Fe++, Cr, Al, Co, Mn, Sc, Ti, or Vn;
Z = Si, Al, or a combination of both.
Crystal Form: Stubby, prismatic crystals.
Crystal System: Pyroxenes are divided into the Clinopyroxene Subgroup (monoclinic) and the Orthopyroxene Subgroup (orthorhombic).
Color: Commonly dark green, dark brown or black. Some, such as jadeite and spodumene, occur in a range of colors
Streak: White
Luster: Vitreous (glassy) to dull
Fracture: Irregular/Uneven, Sub-Conchoidal
Cleavage: Most pyroxene minerals exhibit two directions of cleavage that intersect at approximately 87o and 93o. Cleavage fragments often have a nearly square cross-section
Hardness: 5 to 7 on Moh’s scale
Density/Specific Gravity: 3 - 4 g/cm3
Magnetism: N/A
Taste: N/A
Hydrochloric acid: N/A
Radioactivity: N/A
Fluorescence: Fluorescent amphiboles have been noted, from Franklin, NJ. Greenish blue, long wave UV.
Distinguishing Physical Properties:
Cleavage: 2 pronounced cleavages on some samples ~ 90o
Color: dark or dull green
Hardness: hard (5-7)
Difficult: easily confused with amphiboles; if present, the right angle cleavage can differentiate
Photograph Attribution: Pyroxene specimen photograph by Sean C. Murphy, 2020.