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Black Minerals

The most common and significant ones

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Many minerals are gray or metallic, but this list is for minerals that are black or nearly black. First, be sure you're looking at actual minerals (visible grains or crystal formations) with a black or nearly black color, not a smooth-textured black rock. Inspect the color closely, in good light, for greenish or brownish or bluish tinges. Try to identify the rock type (start with "How to Look at a Rock" and determine, or at least make your best guess, whether it's an igneous, sedimentary or metamorphic rock). That is important for many black minerals, which favor a particular rock class. Black minerals are relatively easy to identify once you've learned about the most common ones. See them here in alphabetical order, along with their typical luster and hardness.

Augite

Close-up of augite
DEA/C.BEVILACQUA/De Agostini Picture Library/Getty Images
Augite is the usual black or brownish-black pyroxene mineral of the dark igneous rocks and some high-grade metamorphic rocks. Its crystals and cleavage fragments are nearly rectangular in cross section (87° and 93°), the main way to distinguish it from hornblende. Luster glassy; hardness 5 to 6.

Biotite

Geology Guide photo
This mica mineral forms shiny, flexible flakes of a deep black or brownish-black color. Large "book" crystals occur in pegmatites and it is widespread in other igneous and metamorphic rocks; tiny detrital flakes may be found in dark sandstones. Luster glassy to pearly; hardness 2.5 to 3.

Chromite

Courtesy Lazurite under Creative Commons
Chromite is a chromium-iron oxide found in pods or veins in bodies of peridotite and serpentinite. It also may be segregated in thin layers near the bottom of large plutons, former bodies of magma. It may resemble magnetite, but it rarely forms crystals, is only weakly magnetic and has a brown streak. Luster submetallic; hardness 5.5.

Hematite

Geology Guide photo
Hematite, an iron oxide, is the most common black or brownish-black mineral in sedimentary and low-grade metasedimentary rocks. It varies greatly in form and appearance, but in every case hematite produces a reddish streak. Luster dull to semimetallic; hardness 1 to 6.

Hornblende

Geology Guide photo
Hornblende is the typical amphibole mineral in igneous and metamorphic rocks. Look for glossy black or dark green crystals and cleavage fragments forming flattened prisms in cross section (corner angles of 56° and 124°). Crystals may be short or long, and even needlelike in amphibolite schists. Luster glassy; hardness 5 to 6.

Ilmenite

Courtesy Rob Lavinsky via Wikimedia Commons
Crystals of this titanium oxide mineral are sprinkled in many igneous and metamorphic rocks, but they're sizable only in pegmatites. Ilmenite is weakly magnetic and produces a black or brownish streak. Its color can range into dark brown or red. Luster submetallic; hardness 5 to 6.

Magnetite

Geology Guide photo
Magnetite 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, and shaped in octahedrons or dodecahedrons. The streak is black, but its strong attraction to a magnet is the surefire test. Luster metallic; hardness 6.

Pyrolusite/Manganite/Psilomelane

Courtesy wanderflechten under Creative Commons
These manganese oxide minerals usually form massive ore beds or veins. The mineral forming black dendrites between sandstone beds is typically pyrolusite; crusts and lumps are typically called psilomelane. In all cases the streak is sooty black. It releases chlorine gas in hydrochloric acid. Luster metallic to dull; hardness 2 to 6.

Rutile

Courtesy Graeme Churchard under Creative Commons
The titanium oxide mineral rutile usually forms long, striated prisms or flat plates, as well as golden or reddish whiskers inside "rutilated" quartz. Its crystals are widespread in coarse-grained igneous and metamorphic rocks. Its streak is light brown. Luster metallic to adamantine; hardness 6 to 6.5.

Stilpnomelane

Geology Guide photo
This uncommon glittering black mineral, related to the micas, is found primarily in high-pressure metamorphic rocks (blueschist or greenschist) with high iron content. Unlike biotite, its flakes are brittle rather than flexible. Luster glassy to pearly; hardness 3 to 4.

Tourmaline

Geology Guide photo
Tourmaline is common in pegmatites; it also is found in coarse-grained granitic rocks and some high-grade schists. It typically forms prism-shaped crystals with a cross section shaped like a triangle with bulging sides. Unlike augite or hornblende, tourmaline has poor cleavage. It's also harder than those minerals. Clear and colored tourmaline is a gemstone; the typical black form is also called schorl. Luster glassy; hardness 7 to 7.5.

Other Black Minerals

Neptunite — Geology Guide photo
Uncommon black minerals include allanite, babingtonite, columbite/tantalite, neptunite, uraninite, and wolframite. Many other minerals may occasionally take on a black color, whether they are ordinarily green (chlorite, serpentine), brown (cassiterite, corundum, goethite, sphalerite) or other colors (diamond, fluorite, garnet, plagioclase, spinel).
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