PHYSICAL PROPERTIES:
Chemistry: PbMoO4
Composition: Lead Molybdate
Class: Sulfates
Crystal system: tetragonal; 4/m or 4
Fracture: conchoidal
Hardness: 2.7-3
Specific gravity: 6.8
Refractive Index: 2.28-2.40
Luster: vitreous
Streak: white
Cleavage: perfect in one direction
Color: Red, orange, yellow, brown, gray,
almost white
Transparency: Crystals are transparent to translucent
Associated Minerals: galena, limonite,
mimetite, pyromorphite, smithsonite and vanadinite.
COMPOSITION:
Lead molybdate (60.7% PbO, 39.3% MoO3)
DISTINGUISHING CHARACTERISTICS:
The brilliant colors together with the tabular development of the
crystals are characteristic of this mineral. Making it one of the easiest
minerals to recognize. There is almost no other minerals that it can
be confused with.
ENVIRONMENT:
A secondary mineral forming near the surface in lead veins. Wulfenite
develops best in dry climates, where weathering has extended
fairly deep. The American Southwest and Mexico are particularly notable
for their occurrences of wulfenite.
CRYSTAL DESCRIPTION:
Wulfenite almost always forms in crystals, usually tabular, often very
thin. Sometimes octahedral pinacoidal plates with pyramidal faces. At
times the pyramids become prominent and psuedo-dipyramidal crystal habits
are seen, sometimes because of twinning. Prismatic faces are also seen
and can make psuedo-cubic crystals. Also encrusting and cavernous aggregates
due to intergrowth of crystal plates. Although most crystals don't show
it clearly, the bottom pyramidal faces slant at a different angle from
the top pyramidal faces. This demonstrates the symmetry of just 4. However,
other tests of its symmetry show a 4/m symmetry which adds to wulfenite's
interest On the large thin plates the prism faces are often irregularly
developed so that the crystals are not sharply bounded.
TESTS:
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 in hot hydrochloric acid becomes frosted
on the surface, turns blue when removed and rubbed with steel needle
while still wet.
LOCALITIES:
Brilliant orange crystals were found at the Red Cloud
Mine, in Yuma County, Arizona. There are many occurrences in the Southwest,
too many to list. The brown crystals of Los Lamentos, Chihuahua, Mexico,
tend to be more prismatic in habit than is common. A rare and unusual
eastern United States occurrence was at a lead mine in Southampton,
Massachusetts; and at Phoenixville, Pennsylvania, with pyromorphite.
Other notable Occurrences include Morocco; and Tsumeb in the African
state of Nambia.
USES:
A minor ore of molybdenum and as mineral specimens.
FACTS & HISTORY:
The first occurrence, in Carinthia, Austria, was described by Xavier
Wulfen in 1785, who drew recognizable pictures of many prismatic and
pyramidal crystals, before the importance of the crystal shape was widely
known.
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