Minerals & Crystals Codexery

Hornblende

A dark amphibole series common in igneous and metamorphic rocks.

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It typically appears as an opaque green, dark green, brown, or black mineral with a hardness of 5–6 and a specific gravity of 3.0 to 3.6.[1] The term "hornblende" is a general field name for dark amphiboles, not a formally recognized mineral species, and it describes a complex series of inosilicate minerals.[2]

Key facts and history

Its cleavage planes intersect at 56° and 124° angles, distinguishing it from pyroxenes which cleave at 87° and 93°.[3] The mineral is built around double chains of silica tetrahedra that extend the length of the crystal.[4] Hornblende is part of the calcium-amphibole group and is highly variable in composition, including at least five solid solution series.[4] Titanium, manganese, or chromium can substitute for some cations, and oxygen, fluorine, or chlorine for some hydroxide.[4]

According to Nesse's 2000 "Introduction to mineralogy", hornblende appears as diamond-shaped prismatic or bladed crystals, or as irregular grains and fibrous masses.[1] The name "hornblende" likely comes from the German words Horn ('horn') and blende ('deceive'), referencing its deceptive resemblance to ore minerals that contain metal.[5]

What the research sources say

Klein's 1993 "Manual of mineralogy" describes a solid solution series between hornblende and tremolite–actinolite at elevated temperature, with a miscibility gap at lower temperatures that often produces exsolution lamellae of grunerite.[6] The 1997 "Glossary of Geology" describes oxyhornblende as a variety where most iron is oxidized to the ferric state, and charge balance is maintained by oxygen ions replacing hydroxide.[7] The same 1997 "Glossary of Geology" indicates that oxyhornblende is often rich in titanium and occurs nearly only in volcanic rocks, where it is sometimes termed basaltic hornblende.[7]

References

  1. 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
  2. Wikipedia, "Hornblende" (CC BY-SA 4.0) en.wikipedia.org
  3. 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
  4. Wikipedia, "Hornblende" (CC BY-SA 4.0), which cites: Nesse 2000, p. 277–279 (original not read by us) en.wikipedia.org
  5. 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
  6. 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
  7. 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

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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Sources

Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.

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