Science, Tech, Math › Science Identifying Black Minerals Tips on Where to Look and What to Look For Share Flipboard Email Print Science Geology Types Of Rocks Landforms and Geologic Features Geologic Processes Plate Tectonics Chemistry Biology Physics Astronomy Weather & Climate By Andrew Alden Geology Expert B.A., Earth Sciences, University of New Hampshire Andrew Alden is a geologist based in Oakland, California. He works as a research guide for the U.S. Geological Survey. our editorial process Andrew Alden Updated July 29, 2019 Pure black minerals are less common than other types of minerals and can sometimes be difficult to recognize if you don't know what to look for. However, by carefully observing such things as grain, color, and texture and studying their most notable characteristics—including luster and hardness as measured on the Mohs Scale—you should soon be able to identify many of these geological rarities. Augite DEA/C.BEVILACQUA/De Agostini Picture Library / Getty Images Augite is a standard black or brownish-black pyroxene mineral of dark igneous rocks and some high-grade metamorphic rocks. Its crystals and cleavage fragments are nearly rectangular in cross-section (at angles of 87 and 93 degrees). These are the main things that distinguish it from hornblende (see below). Characteristics: Glassy luster; hardness of 5 to 6. Biotite De Agostini Picture Library / Getty Images 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 found in dark sandstones. Characteristics: Glassy to pearly luster; hardness of 2.5 to 3. Chromite De Agostini/R. Appiani / Getty Images Chromite is a chromium-iron oxide found in pods or veins in bodies of peridotite and serpentinite. (Look for brown streaks.) 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 rarely forms crystals and is only weakly magnetic. Characteristics: Submetallic luster; hardness of 5.5. 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. Characteristics: Dull to semimetallic luster; hardness of 1 to 6. 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 degrees). Crystals may be short or long, and even needle-like in amphibolite schists. Characteristics: Glassy luster; hardness of 5 to 6. Ilmenite Rob Lavinsky, iRocks.com/Wikimedia Commons / CC BY-SA 3.0 Crystals of this titanium-oxide mineral are sprinkled in many igneous and metamorphic rocks, but they're sizeable only in pegmatites. Ilmenite is weakly magnetic and produces a black or brownish streak. Its color can range from dark brown to red. Characteristics: Submetallic luster; hardness of 5 to 6. Magnetite Andreas Kermann / Getty Images 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: Metallic luster; hardness of 6. Pyrolusite/Manganite/Psilomelane DEA/PHOTO 1 / Getty Images These manganese-oxide minerals usually form massive ore beds or veins. The mineral-forming black dendrites between sandstone beds are generally pyrolusite. Crusts and lumps are typically called psilomelane. In all cases, the streak is sooty black. These minerals release chlorine gas when exposed to hydrochloric acid. Characteristics: Metallic to dull luster; hardness of 2 to 6. Rutile DEA/C.BEVILACQUA / Getty Images 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. Characteristics: Metallic to adamantine luster; hardness of 6 to 6.5. Stilpnomelane Kluka/Wikimedia Commons / CC-BY-SA-3.0 This uncommon glittering black mineral, related to the micas, is found primarily in high-pressure metamorphic rocks with high iron content such as blueschist or greenschist. Unlike biotite, its flakes are brittle rather than flexible. Characteristics: Glassy to pearly luster; hardness of 3 to 4. Tourmaline lissart / Getty Images Tourmaline is common in pegmatites. It's also 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 and is also harder than those minerals. Clear and colored tourmaline is a gemstone. The typical black form is sometimes called schorl. Characteristics: Glassy luster; hardness of 7 to 7.5. Other Black Minerals De Agostini/A. Rizzi / Getty Images Uncommon Black minerals include allanite, babingtonite, columbite/tantalite, neptunite, uraninite, and wolframite. Many other minerals may occasionally take on a black appearance, whether they are ordinarily green (chlorite, serpentine), brown (cassiterite, corundum, goethite, sphalerite), or other colors (diamond, fluorite, garnet, plagioclase, spinel).