Hornblende
A dark amphibole mineral series common in igneous and metamorphic rocks.
It typically appears as an opaque green, dark green, brown, or black mineral with a hardness of 5–6 and specific gravity of 3.0 to 3.6.[1] Hornblende is a term for dark amphiboles, not a single mineral, and belongs to a complex inosilicate series.[2]
Quick Facts
- Category
- Silicate mineral
- Formula
- Ca2(Mg,Fe,Al)5(Al,Si)8O22(OH)2
- IMA symbol
- Hbl
- Habit
- Hexagonal/granular
- System
- Monoclinic
- Symmetry
- C2/m
- Cleavage
- Imperfect at 56° and 124°
- Fracture
- Uneven
Facts from the source article.
Key facts and history
Hornblende is built around double chains of silica tetrahedra, forming an inosilicate (chain silicate) mineral.[3] Its cleavage planes intersect at 56° and 124° angles, distinguishing it from pyroxenes, which cleave at 87° and 93°.[4] Hornblende is part of the calcium-amphibole group and is highly variable in composition, including at least five solid solution series.[3] Titanium, manganese, or chromium can substitute for some cations, and oxygen, fluorine, or chlorine for some hydroxide.[3]
The name "hornblende" likely comes from the German words Horn ('horn') and blende ('deceive'), referencing its resemblance to ore minerals or its shine.[5] Double chains of silica tetrahedra run the crystal's length, connected to adjacent chains by metal ions.[3] Even with optical or X-ray techniques, telling apart the various chemical types is nearly impossible; an electron microprobe is necessary for detailed chemical analysis.[3] When magma is cooler and richer in silica and water, hornblende forms instead of pyroxene.[3]
Oxyhornblende, also called basaltic hornblende, is a variety where iron is mostly in the ferric state and is found nearly only in volcanic rocks.[6]
What the research sources say
The 1997 "Glossary of Geology" defines oxyhornblende as a variety in which most iron has been oxidized to ferric iron, with charge balance preserved by oxygen substituting for hydroxide.[6] According to the same source, oxyhornblende usually has a high titanium content.[6] Klein's 1993 "Manual of mineralogy" indicates that at high temperatures, hornblende and tremolite–actinolite form a solid solution series.[7]
References
- Wikipedia, "Hornblende" (CC BY-SA 4.0), which cites: Nesse, "Introduction to mineralogy", Oxford University Press, 2000, p. 285–286 (we also read that source) en.wikipedia.org
- Wikipedia, "Hornblende" (CC BY-SA 4.0) en.wikipedia.org
- Wikipedia, "Hornblende" (CC BY-SA 4.0), which cites: Nesse 2000, p. 277–279 (original not read by us) en.wikipedia.org
- Wikipedia, "Hornblende" (CC BY-SA 4.0), which cites: Pough, "A Field Guide To Rocks and Minerals", Houghton Mifflin, 1976, p. 249 (original not read by us) en.wikipedia.org
- Wikipedia, "Hornblende" (CC BY-SA 4.0), which cites: Anthony, "Ferrohornblende", Handbook of Mineralogy, 2005; Cook, "Pocket Guide - Rocks and Minerals", Larousse, 1995, p. 110 (original not read by us) en.wikipedia.org
- Wikipedia, "Hornblende" (CC BY-SA 4.0), which cites: "Glossary of geology.", American Geological Institute, 1997; Nesse 2000, p. 277–279 (we also read that source) en.wikipedia.org
- Wikipedia, "Hornblende" (CC BY-SA 4.0), which cites: Klein, "Manual of mineralogy : (after James D. Dana)", Wiley, 1993, p. 496–497 (we also read that source) en.wikipedia.org
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Hornblende (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.
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