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Botryoidal Mimetite

The Mineral mimetite




Mimetite is a member of the Apatite group, a group of isomorphous hexagonal minerals. It is very similar in structure and appearance to Pyromorphite, and may be partially replaced by it. In fact, sometimes Mimetite and Pyromorphite are virtually indistinguishable from each other and may be wrongly labeled as the other. Mimetite is also structurally similar to Vanadinite, and may also be partially replaced by it. The intermediary member between Mimetite and Vanadinite is known as Endlichite.
Chemical Formula Pb5(AsO4)3Cl
Composition Lead chloro-arsenate. The arsenate radical (AsO4) may be partially replaced by a phosphate radical (PO4) or vanadate radical (VO4), and thereby forms a series with Pyromorphite and Vanadinite.
Variable Formula Pb5([As,P,V]O4)3Cl
Color Light yellow, lemon-yellow, dark yellow, orange, brown, reddish-brown, and yellow-green. Rarely colorless or white. May also be multicolored orange, yellow, and greenish-yellow.
Streak White
Hardness 3.5 - 4
Crystal System Hexagonal
Crystal Forms
and Aggregates
Occurs in small, slender, prismatic crystals and in mammilary and botryoidal crusts. A rare habit is large, stubby, hexagonal crystals. Also occurs as wedge-shaped crystals, acicular, radiating, reniform, encrusting, and in curvy and fibrous aggregates. Some larger crystals may be hollowed out on the ends or have a hopper growth pattern.
Transparency Transparent to translucent
Specific Gravity 7.0 - 7.3
Luster Resinous to adamantine
Cleavage Indiscernible
Fracture Subconchoidal to uneven
Tenacity Brittle
Complex Tests 1) Dissolves in hydrochloric acid
2) Gives off a strong garlic odor if heated (fumes are poisonous!)
In Group Phosphates; Arsenates
Striking Features Color, crystal habits, mineral associates, and mode of occurrence.
Environment As a secondary mineral in the oxidation zone of lead ore deposits.
Rock Type Sedimentary, Metamorphic
Popularity (1-4) 2
Prevalence (1-3) 3
Demand (1-3) 1


Mimetite AUCTIONS

VARIETIES
 -  Wedge-shaped, orange-yellow to brown variety of Mimetite with curved faces.
POLYMORPHS
Clinomimetite


USES
Mimetite is a minor ore of lead where it occurs with more abundant lead minerals. It is also a popular mineral among collectors.

NOTEWORTHY LOCALITIES
A classic German locality is Johanngeorgenstadt, Saxony, Germany, where large tabular crystals had once come from. These crystals are very hard to obtain today as they are all from old collections and command extremely high prices. Small radiating acicular Mimetite groupings come from the Clara Mine, Oberwolfach, Baden-Württemberg, Germany. An old-time English locality is Wheal Unity, Gwennap, Cornwall, England; and the most famous Campylite occurrence in the world is the Dry Gill Mine, Caldbeck Fells, Cumbria, England.

Spiky aggregates of Mimetite crystals come from Tsumeb, Namibia; and very large whitish-yellow crystals come from Mt. Bonnie, Northern Territory, Australia. Beautiful lustrous and gemmy crystals come from the Pingtouling Mine, Liannan Co, Guangdong Province, China; and from Hat Yai, Thailand

Mexico has several outstanding locations for this mineral. Many Mexican occurrences have Mimetite in the form of mammilary or botryoidal groupings, expecially San Pedro Corralitos, Chihuahua; and Santa Eulalia, Chihuahua. Spiky crystals and green botryoidal masses come from a new find in the famous Mapimi Mine in Durango, Mexico. Deep orange radial encrustions occur in Cerro Prieta, Sonora, also associated with Wulfenite.

In the U.S., the good locations are all but limited to several Arizona mines, specifically the the Rowley Mine, near Theba, Maricopa Co.; the Mammoth-Saint Anthony Mine, Tiger, Pinal Co.; the No. 79 Mine, near Hayden, Gila Co.; and the Sammy Dog Mine, Silver Bell District, Pima Co.

COMMON MINERAL ASSOCIATIONS
Wulfenite, Vanadinite, Limonite, Galena, Barite, Anglesite, Hemimorphite, Arsenopyrite

DISTINGUISHING SIMILAR MINERALS
Pyromorphite - Usually greener in color. Otherwise cannot be distinguished with practical methods.
Vanadinite - Usually redder in color, has a slightly yellow streak, and is slightly softer. Otherwise cannot be distinguished with practical methods.
Apatite - Harder (5).


mimetite PHOTOS
 
ADDITIONAL RESOURCES
 
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