Pure black minerals are less mutual than other types of minerals and can sometimes be difficult to recognize if yous don’t know what to look for. Withal, past advisedly observing such things as grain, colour, and texture and studying their near notable characteristics—including luster and hardness as measured on the Mohs Scale—yous should soon exist able to identify many of these geological rarities.
Augite is a standard black or chocolate-brown-black pyroxene mineral of nighttime igneous rocks and some loftier-class metamorphic rocks. Its crystals and cleavage fragments are nearly rectangular in cross-section (at angles of 87 and 93 degrees). These are the primary things that distinguish information technology from hornblende (see below).
Characteristics: Glassy luster; hardness of v to 6.
This mica mineral forms shiny, flexible flakes that are deep black or brownish-black in color. Large book crystals occur in pegmatites and it is widespread in other igneous and metamorphic rocks, while tiny detrital flakes may be institute in dark sandstones.
Characteristics: Glassy to pearly luster; hardness of 2.5 to 3.
Chromite is a chromium-atomic number 26 oxide found in pods or veins in bodies of peridotite and serpentinite. (Look for brown streaks.) It may also be segregated in thin layers nigh the bottom of large plutons, or former bodies of magma, and is sometimes found in meteorites. It may resemble magnetite but rarely forms crystals and is only weakly magnetic.
Characteristics: Submetallic luster; hardness of 5.5.
Hematite, an iron oxide, is the most mutual black or brownish-black mineral in sedimentary and depression-grade metasedimentary rocks. It varies greatly in form and appearance, but all hematite produces a crimson streak.
Characteristics: Dull to semimetallic luster; hardness of 1 to 6.
Hornblende is the typical amphibole mineral in igneous and metamorphic rocks. Look for sleeky black or dark light-green crystals and cleavage fragments forming flattened prisms in cross-section (corner angles of 56 and 124 degrees). Crystals may be brusque or long, and even needle-like in amphibolite schists.
Characteristics: Glassy luster; hardness of 5 to 6.
Crystals of this titanium-oxide mineral are sprinkled in many igneous and metamorphic rocks, but they’re sizeable just in pegmatites. Ilmenite is weakly magnetic and produces a black or brownish streak. Its color tin range from night brown to red.
Characteristics: Submetallic luster; hardness of 5 to 6.
Magnetite (or lodestone) is a common accessory mineral in coarse-grained igneous rocks and metamorphic rocks. It may be gray-black or have a rusty coating. Crystals are common, with striated faces shaped in octahedrons or dodecahedrons. Look for a black streak and a strong attraction to a magnet.
Characteristics: Metal luster; hardness of 6.
These manganese-oxide minerals usually form massive ore beds or veins. The mineral-forming black dendrites between sandstone beds are by and large pyrolusite. Crusts and lumps are typically called psilomelane. In all cases, the streak is sooty blackness. These minerals release chlorine gas when exposed to hydrochloric acid.
Characteristics: Metallic to dull luster; hardness of 2 to 6.
The titanium-oxide mineral rutile usually forms long, striated prisms or apartment plates, as well as golden or cherry whiskers inside rutilated quartz. Its crystals are widespread in coarse-grained igneous and metamorphic rocks. Its streak is light brown.
Characteristics: Metal to adamantine luster; hardness of six to 6.5.
This uncommon glittering black mineral, related to the micas, is found primarily in high-pressure metamorphic rocks with loftier iron content such as blueschist or greenschist. Unlike biotite, its flakes are brittle rather than flexible.
Characteristics: Burnished to pearly luster; hardness of 3 to 4.
Tourmaline is common in pegmatites. It’s also constitute in coarse-grained granitic rocks and some loftier-grade schists. Information technology typically forms prism-shaped crystals with a cantankerous-department shaped like a triangle with bulging sides. Unlike augite or hornblende, tourmaline has poor cleavage and is also harder than those minerals. Articulate and colored tourmaline is a gemstone. The typical black form is sometimes called schorl.
Characteristics: Glassy luster; hardness of vii to 7.5.
Other Blackness Minerals
Uncommon Black minerals include allanite, babingtonite, columbite/tantalite, neptunite, uraninite, and wolframite. Many other minerals may occasionally take on a black advent, whether they are normally dark-green (chlorite, serpentine), dark-brown (cassiterite, corundum, goethite, sphalerite), or other colors (diamond, fluorite, garnet, plagioclase, spinel).