Hornblende Archives - Cochise College Geology

Hornblende

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Chemical Group: Silicate-amphibole group

Chemical Formula: NaCa₂(Mg,Fe,Al)₅(Si,Al)₈O₂₂(OH)₂

Color: Dark green, dark brown, black Streak: White to gray

Luster: Vitreous

Hardness: 6 Specific Gravity: 3.0 to 3.4

Cleavage: 2 directions at an angle of 124 degrees from each other

Crystal Forms and Habits: Monoclinic system. Hornblende forms prismatic crystals

Mineral Associations: Diorites, syenites and is common in medium grade metamorphic rocks.

Identifying Characteristics: Elongated crystals, dark color, cleavage angles

Toxicity: When-swallowed: low When-inhaled: high

Additional Information: As an exciting, colorful mineral, hornblende doesn’t make the list. Hornblende is the most common member of the amphibole family of silicate minerals. Besides silica, it has a little bit of everything else in its chemistry: ferrous and ferric iron, aluminum, calcium, manganese, magnesium, and alkalis. Hornblende forms prismatic, dark brown to black, small crystals in many igneous
rocks. It is most commonly confused with the mineral augite that forms shorter, stubby crystals. Hornblende can be distinguished from augite by its cleavage; the two cleavage planes in augite are nearly at right angles, while the two cleavage planes in hornblende are at an angle of 124 degrees.

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Photos

Hornblende 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

hornblende-black crystalline mass — Hornblende - Black Crystalline Mass

hornblende-black elongated crystal in white feldspar — Hornblende - Black Elongated Crystal in White Feldspar

hornblende-black-massive — Hornblende - Black - Massive

hornblende-black elongated crystal — Hornblende - Black Elongated Crystal

hornblende-cluster of black crystals — Hornblende - Cluster of Black Crystals

hornblende-cross-sectional view of crystal — Hornblende - Cross-Sectional View of Crystal

hornblende-elongated greenish black crystals — Hornblende - Elongated Greenish Black Crystals

hornblende-dark brown crystalline mass — Hornblende - Dark Brown Crystalline Mass

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