Hornblende
Image: Nessa Eull (CC0)
Mineral NameHornblende
Chemical FormulaCa2(Mg,Fe,Al)5(Al,Si)8O22(OH)2
Mohs Hardness5
Crystal Systemmonoclinic
Lustervitreous
Streak Colorwhite to grayish-white
CleavagePerfect prismatic on {110} at 56° and 124°
Fractureuneven
Specific Gravity3.2
Colorsblack, dark green, dark brown
Transparencyopaque to translucent
Type LocalityQuebec, Canada
Mineral GroupSilicates (Amphibole Group)
Usesrock-forming mineral, scientific interest
Associated Mineralsapatite, calcite, quartz, feldspar, mica, pyroxene
Raritycommon
Description
Hornblende typically forms as black to dark green, prismatic to blocky crystals with a vitreous luster. In this specimen, it appears as black masses accompanying brown apatite and whitish calcite.
Geological Context
Hornblende is a common rock-forming mineral found in various igneous rocks such as granite, diorite, gabbro, and basalt, as well as in metamorphic rocks like amphibolite, gneiss, and schist. It forms during the crystallization of magma or through the metamorphism of pre-existing rocks.
