How to Identify Black Minerals

How to Identify the Most Common and Significant Black Minerals

Pure black minerals aren't all that common. Often a mineral may look black but, after a good wash, may turn out to be green or gray. If you do find a black mineral, though, even if it includes touches of colored crystals, there are some simple ways to identify it.

I Have a Black Mineral - What Is It? 

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.

1
Augite

Close-up of augite
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°). This is the main way to distinguish it from hornblende, which is discussed later in this list.

Glassy luster; hardness of 5 to 6.

2
Biotite

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.

Glassy to pearly luster; hardness of 2.5 to 3.

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 may also be segregated in thin layers near the bottom of large plutons, or former bodies of magma, and is sometimes found in meteorites. It may resemble magnetite, but it rarely forms crystals, is only weakly magnetic and has a brown streak.

Submetallic(**link?**) luster; hardness of 5.5.

4
Hematite

Hematite, oxide
Hematite. De Agostini Picture Library / Getty Images

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 all hematite produces a reddish streak.

Dull to semimetallic luster; hardness of 1 to 6.

5
Hornblende

Hornblende, silicate
Hornblende. De Agostini / C. Bevilacqua / Getty Images

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.

Glassy luster; hardness of 5 to 6.

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.

Submetallic luster; hardness of 5 to 6.

7
Magnetite

Magnetite
Magnetite. Andreas Kermann / Getty Images

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. 

Another name for magnetite is lodestone.

Metallic luster; hardness of 6.

8
Pyrolusite/Manganite/Psilomelane

Pyrolusite
Pyrolusite. DEA / PHOTO 1 / Getty Images

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.

Metallic to dull luster; hardness of 2 to 6.

9
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.

Metallic to adamantine luster; hardness of 6 to 6.5.

10
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.

Glassy to pearly luster; hardness of 3 to 4.

11
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.

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Glassy luster; hardness of 7 to 7.5.

12
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).