Guide to Identifying Yellow Minerals

Amber

Amber tends toward honey colors, in keeping with its origin as tree resin. It may also be root-beer brown and nearly black. It's found in relatively young (Cenozoic) sedimentary rocks in isolated lumps. Being a mineraloid rather than a true mineral, amber never forms crystals.

Luster resinous; hardness 2 to 3.

Calcite

Calcite, the main ingredient of limestone, is usually white or clear in its crystalline form in sedimentary and metamorphic rocks. But massive calcite found near the Earth's surface very often takes on yellowish colors from iron oxide staining. 

Luster waxy to glassy; hardness 3.

Carnotite

Carnotite is a uranium-vanadium oxide mineral, K₂(UO₂)₂(V₂O₈)·H₂O, that occurs scattered around the western United States as a secondary (surface) mineral in sedimentary rocks and in powdery crusts. Its bright canary yellow may also blend into orange. Carnotite is of surefire interest to uranium prospectors, marking the presence of uranium minerals deeper down. It's mildly radioactive, so you may want to avoid mailing it to people.

Luster earthy; hardness indeterminate.

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Feldspar

Feldspar is extremely common in igneous rocks and somewhat common in metamorphic and sedimentary rocks. Most feldspar is white, clear or gray, but colors from ivory to light orange in a translucent feldspar are typical of alkali feldspar. When inspecting feldspar, take care to find a fresh surface. Weathering of the black minerals in igneous rocks—biotite and hornblende—tends to leave rust stains.

Luster glassy; hardness 6.

Gypsum

Gypsum, the most common sulfate mineral, is typically clear when it forms crystals, but it also may have light earthy tones in settings where clays or iron oxides are around during its formation. Gypsum is found only in sedimentary rocks that formed in an evaporitic setting.

Luster glassy; hardness 2.

Quartz

Quartz is almost always white (milky) or clear, but some of its yellow forms are of interest. The most common yellow quartz occurs in the microcrystalline rock agate, although agate is more often orange or red. The clear yellow gemstone variety of quartz is known as citrine; this shade may grade into the purple of amethyst or the brown of cairngorm. And cat's-eye quartz owes its golden sheen to thousands of fine needle-shaped crystals of other minerals.

Sulfur

Pure native sulfur is most commonly found in old mine dumps, where pyrite oxidizes to leave yellow films and crusts. Sulfur also occurs in two natural settings. Large beds of sulfur, occurring underground in deep sedimentary bodies, were once mined, but today sulfur is more cheaply available as a petroleum byproduct. You may also find sulfur around active volcanoes, where hot vents called solfataras breathe out a sulfur vapor that condenses in crystals. It's light yellow color may range to amber or reddish from various contaminants.

Luster resinous; hardness 2.

Zeolites

Zeolites are a suite of low-temperature minerals that collectors can find filling the former gas bubbles (amygdules) in lava flows. They also occur disseminated in tuff beds and salt lake deposits. Several of these (analcime, chabazite, heulandite, laumontite, and natrolite) may assume creamy colors that grade into pink, beige and buff. 

Luster pearly or glassy; hardnesses 3.5 to 5.5.

Other Yellow Minerals

A number of yellow minerals are rare in nature but common in rock shops and at rock and mineral shows. Among these are gummite, massicot, microlite, millerite, niccolite, proustite/pyrargyrite, and realgar/orpiment. Many other minerals may occasionally adopt yellowish colors aside from their usual colors. These include alunite, apatite, barite, beryl, corundum, dolomite, epidote, fluorite, goethite, grossular, hematite, lepidolite, monazite, scapolite, serpentine, smithsonite, sphalerite, spinel, titanite, topaz, and tourmaline.