wulfenite

n.
A usually yellow to orange-brown mineral, PbMoO₄, used as a molybdenum ore.

[German Wulfenit, after Franz Xavier von Wulfen (1728-1805), Austrian mineralogist.]

A mineral consisting of lead molybdate, PbMoO₄. Wulfenite occurs commonly in yellow, orange, red, and grayish-white crystals, with a luster from adamantine to resinous. Wulfenite may also be massive or granular. Its fracture is uneven. Its hardness is 2.7–3 on Mohs scale and its specific gravity 6.5–7. Its streak is white.

Wulfenite is found in numerous localities in the western and southwestern United States. Brilliant orange tabular wulfenite crystals up to 2 in. (5 cm) in size have been found from the Red Cloud and Hamburg mines in Yuma County, Arizona. See also Molybdenum.

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PbMoO
Tetragonal -- Tetragonal pyramidal

Environment

A secondary mineral forming near the surface in lead veins.

Crystal description

Almost always in crystals, usually tabular, often very thin and fragile. Basal plane well developed; occasional third-order pyramid faces make base appear interestingly skewed in relation to the crystal outline. Prismatic and pyramidal habits less frequent. On the large thin plates the prism faces are often irregularly developed so that the crystals are not sharply bounded.

Physical properties

Yellow, orange, brown, gray, almost white and matching streaks. Luster adamantine; hardness 2Ɛ-3; specific gravity 6.8; fracture subconchoidal; cleavage pyramidal good, 2 poor. Very fragile and brittle; transparent to translucent.

Composition

Lead molybdate (60.7% PbO, 39.3% MoO ₃ ).

Test

The brilliant color, high luster, and platy habit make most tests unnecessary. Fuses easily to slag that is yellow when hot, gray when cold. Shiny fragment under a drop of hot hydrochloric acid becomes frosted on the surface, turns blue when rubbed with steel needle while wet.

Distinguishing characteristics

The brilliant colors characteristic of this mineral, together with the tabular development of the crystals, make it one of the easiest minerals to recognize. There is almost nothing with which there is any danger of confusing it except stolzite, the rare tungsten equivalent (PbWO ₄ ).

Occurrence

Best developed in dry climates where weathering has extended fairly deep. The American Southwest and Mexico are particularly notable for their occurrences of wulfenite. (See comment under molybdenite, p. 128, about the fugitive character of Mo solutions.) Solutions bearing ilsemannite could be the source of the molybdenum needed for the wulfenite formation, the origin of which has always been something of a mystery. The most brilliant orange crystals, the hue said to be due to chromium, are still found at the Red Cloud Mine, Yuma Co., Arizona, and at Chah-Kharbose in Iran. There are many occurrences in the Southwest however, far too many to list. The orange to caramel crystals of Los Lamentos, Chihuahua, Mexico, tend to be more prismatic in habit than is common. Rare and unusual e. U.S. occurrences were at a lead mine in Southampton, Massachusetts; and at Phoenixville, Pennsylvania, with the pyromorphite. The thickest crystals of wulfenite are almost colorless (within) 2-in. (5 cm) square ones from M'fouati, Congo Republic, usually coated with quartz, which adheres tightly to the base face (it chips easily from the pyramid faces). Spectacular thin yellow crystals, with orange mimetite, come from the San Francisco Mine in Sonora, Mexico. Cerro Prieto has smaller but similar crystals. Scheelite-like crystals from Broken Hill, New South Wales, will be stolzite.

The first occurrence, in Carinthia, Austria, was described by Xavier Wulfen in 1785, who made recognizable pictures of many prismatic and pyramidal crystals a decade before the importance of the shape of crystals was widely recognized.

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Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: a yellow to orange or brown mineral used as a molybdenum ore

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