Brown Minerals

The most common and significant ones

Brown is a common color for rocks in general at the Earth's surface. It may take careful observation to evaluate a brown mineral, and color may be the least important thing to see. Moreover, brown is a mongrel color that blends into red, green, yellow, white and black. Look at a brown mineral in good light, making sure to inspect a fresh surface, and ask yourself exactly what kind of brown it is. Determine the mineral's luster and be ready to do hardness tests, too. Finally, know something about the rock that the mineral occurs in. Here are the most common possibilities. The first four—clays, two iron oxide minerals, and sulfides—account for nearly all occurrences; the rest are presented in alphabetical order.

Shale, close up.
Gary Ombler/Dorling Kindersley/Getty Images

Clay is a set of minerals with microscopic grains and colors ranging from medium brown to white. It's the main ingredient of shale. It never forms visible crystals. Geologists often nibble on shale; pure clay is a smooth substance with no grittiness on the teeth. Luster dull; hardness 1 or 2. More »

Hematite
Botryoidal hematite. Botryoidal hematite — Andrew Alden photo

The most common iron oxide, hematite ranges from red and earthy, through brown, to black and crystalline. In every form it takes, hematite has a red streak. It may also be slightly magnetic. Suspect it wherever a brown-black mineral appears in sedimentary or low-grade metasedimentary rocks. Luster dull to semimetallic; hardness 1 to 6. More »

Goethite
Goethite. Goethite — Andrew Alden photo

Goethite is fairly common, but seldom concentrated in bulk form. It's much harder than clay, has a yellowish brown streak and is well developed where iron minerals have weathered. "Bog iron" is typically goethite. Luster dull to semimetallic; hardness around 5. More »

Sulfide minerals
Chalcopyrite. Chalcopyrite — Andrew Alden photo

Some of the metal sulfide minerals are typically bronze to brown (pentlandite, pyrrhotite, bornite). Suspect one of these if it occurs along with pyrite or other common sulfides. Luster metallic; hardness 3 or 4. More »

Amber
Amber. Amber — Mersey Viking (Flickr CC BY-NC-SA 2.0)

A fossil tree resin rather than a true mineral, amber is restricted to certain mudstones and ranges in color from honey to the dark brown of bottle glass. It's lightweight, like plastic, and it often contains bubbles, sometimes fossils like insects. It will melt and burn in a flame. Luster resinous; hardness less than 3. More »

Andalusite
Andalusite. Andalusite — -Merce- (Flickr CC BY-NC-SA 2.0)

A sign of high-temperature metamorphism, andalusite may be pink or green, even white, as well as brown. It usually occurs in stubby crystals in schist, with square cross sections that may display a crosslike pattern (chiastolite). Luster glassy; hardness 7.5. More »

Axinite
Axinite. Axinite — Andrew Alden photo

This odd boron-bearing silicate mineral is more readily found in rock shops than in the field, but you might see it in metamorphic rocks near granite intrusions. Its lilac-brown color and flat bladed crystals with striations are distinctive. Luster glassy; hardness around 7. More »

Cassiterite
Cassiterite. Cassiterite — Wikimedia Commons

An oxide of tin, cassiterite occurs in high-temperature veins and pegmatites. Its brown color shades into yellow and black. Even so, its streak is white, and it will feel heavy if you can get a big enough piece to heft in your hand. Its crystals, when broken, typically show bands of color. Luster adamantine to greasy; hardness 6–7. More »

Copper
Copper. Wire Copper — Andrew Alden photo

Copper may be reddish brown due to impurities. It occurs in metamorphic rocks and in hydrothermal veins near volcanic intrusions. Copper should bend like the metal it is, and it has a distinctive streak. Luster metallic; hardness 3. More »

Corundum
Corundum. Corundum — Andrew Alden photo

Its extreme hardness is the surest sign of corundum, along with its occurrence in high-grade metamorphic rocks and pegmatites in six-sided crystals. Its color ranges widely around brown and includes the gemstones sapphire and ruby. Rough cigar-shaped crystals are available in any rock shop. Luster adamantine; hardness 9. More »

Garnet
Garnet. Almandine in Amphibolite — Andrew Alden photo

The common garnet minerals may appear brown in addition to their usual colors. The six main garnet minerals vary in their typical geologic settings, but all have the classic garnet crystal shape, a round dodecahedron. Brown garnets may be spessartine, almandine, grossular or andradite depending on the setting. Luster glassy; hardness 6–7.5. More »

Monazite

Monazite
Monazite. Monazite — Wikimedia Commons

This rare-earth phosphate is uncommon but widespread in pegmatites as flat, opaque crystals that break into splinters. Its color tends toward reddish brown. Because of its hardness, monazite may persist in sands, and the rare-earth metals were once mined from sand deposits. Luster adamantine to resinous; hardness 5.

Phlogopite
Phlogopite. Phlogopite — Wikimedia Commons

A brown mica mineral that is basically biotite without the iron, phlogopite favors marble and serpentinite. One key feature it may display is asterism when you hold a thin sheet against a light. Luster pearly or metallic; hardness 2.5–3. More »

Pyroxene
Pyroxene. Enstatite — US Geological Survey photo

While the most common pyroxene mineral, augite, is black, the diopside and enstatite series are shades of green that may veer over to brown with high iron contents. Look for bronze-colored enstatite in igneous rocks and brown diopside in metamorphosed dolomite rocks. Luster glassy; hardness 5–6. More »

Quartz
Quartz. Quartz — Andrew Alden photo

Brown crystalline quartz may be called cairngorm; its color arises from missing electrons (holes) plus aluminum impurities. More common is the gray variety called smoky quartz or morion. Usually quartz is easy to tell by its typical hexagonal spears with grooved sides and conchoidal fracture. Luster glassy; hardness 7. More »

Siderite
Siderite. Siderite — Forum member Fantus1ca

A brown mineral occurring in carbonate ore veins is usually siderite, iron carbonate. It also may be found in concretions, and sometimes in pegmatites. It has the typical appearance and rhombohedral cleavage of carbonate minerals. Luster glassy to pearly; hardness 3.5–4. More »

Sphalerite
Sphalerite. Sphalerite — Wikimedia Commons

Sulfide ore veins in rocks of all types are the typical home of this zinc mineral. Its iron content gives sphalerite a color range of yellow through red-brown to black. It may form chunky crystals or granular masses. Look for galena and pyrite with it. Luster adamantine to resinous; hardness 3.5–4. More »

Staurolite
Staurolite. Staurolite — Andrew Alden photo

Perhaps the easiest brown crystalline mineral to learn, staurolite is a silicate found in schist and gneiss as isolated or twinned crystals ("fairy crosses"). Its hardness will distinguish it if there's any doubt. Found in any rock shop, too. Luster glassy; hardness 7–7.5. More »

Topaz
Topaz. Topaz — Andrew Alden photo

This familiar rock-shop item and gemstone may be seen in pegmatites, high-temperature veins and in rhyolite flows where its clear crystals line gas pockets. Its brown color is light and tends toward yellow or pink. Its great hardness and perfect basal cleavage are clinchers. Luster glassy; hardness 8. More »

Zircon
Zircon. Zircon — Andrew Alden photo

A few small zircon crystals are found in many granites and sometimes in marble and pegmatites. Geologists prize zircon for its use in dating rocks and studying early Earth history. Although zircon gemstones are clear, most zircon in the field is dark brown. Look for bipyramidal crystals or short prisms with pyramidal ends. Luster adamantine or glassy; hardness 6.5–7.5. More »

Colored minerals
Colored minerals. Colored minerals — Andrew Alden photo

Brown is an occasional color for many minerals, whether they are typically green (apatite, epidote, olivine, pyromorphite, serpentine) or white (barite, calcite, celestine, gypsum, heulandite, nepheline) or black (biotite) or red (cinnabar, eudialyte) or other colors (hemimorphite, mimetite, scapolite, spinel, wulfenite). Observe which way the brown color tends, and try one of those possibilities. More »

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Alden, Andrew. "Brown Minerals." ThoughtCo, Feb. 28, 2017, thoughtco.com/brown-minerals-examples-1440939. Alden, Andrew. (2017, February 28). Brown Minerals. Retrieved from https://www.thoughtco.com/brown-minerals-examples-1440939 Alden, Andrew. "Brown Minerals." ThoughtCo. https://www.thoughtco.com/brown-minerals-examples-1440939 (accessed September 21, 2017).