Physical Properties (1) GroupSilicates-Inosilicates ColorGreen, Black Crystal HabitPrismatic Crystal System Monoclinic CleavagePerfect FractureUneven, Brittle Hardness5-6 LusterVitreous StreakWhite to Gray Specific Gravity TransparencyTranslucent to Opaque Optical Properties (3 & 7) BirefringenceRanges from.018 to.028 Interference Colors Shades of green, yellow, and brown Extinction AngleSymmetrical to cleavage Index of Refraction N α : N β : N γ : PleochroismGreen or brown Optic SignOptically negative or positive 2V AngleRanges from 52 degrees to 85 degrees TwinningSimple and lamellar twinning ReliefHigh positive relief We can use amphiboles (Such as Hornblende) to help identify an unknown igneous rock (8). Chemical Composition: (CA,Na) 2-3 (Mg, Fe, Al) 5, Si 6, (Si,Al) 2, O 22 (OH) 2 This image shows one of Hornblende’s end members, ferrohornblende (11). This image shows one of hornblende’s end members,magnesiohornblende (12). These images show rare example or hornblende crystals ( & 10). French Mineralogist René-Just Haüy (9) Hornblende’s crystallographic axes (7) This is hornblende in a thin section and in PPL (Plain Polarized Light) (3). This image shows Hornblende’s 60°/120° cleavage (3) This thin section image shows hornblende in XPL (Cross Polarized Light) (3). This thin section image shows Hornblende’s twinning (5)

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Hornblende Like the essential building block of plagioclase, hornblende is actually a member of the solid solution series for amphiboles. Hornblende is the most common occurring amphibole in the canyon and is black or dark green in color. When it fractures, it tends to break at angles of either 60 or120 degrees. It contains significant amounts of potassium and fluorite in its chemical formula, which helps determine the color of the mineral. It sometimes forms large masses known as amphibolite or hornblende schists that are made up of thin, black parallel aligned, needle-like crystals. It is difficult to find any large individual crystals. The name comes from the German miner's term "horn" possibly in reference to the color of horn and "blenden" which means to deceive. This seems to have come from the fact that the mineral mimics the more valuable metallic ores, but doesn't produce a commercial viable metal. Hornblende makes up one of the types of schists in the canyon.