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Mansfieldite

Named to honor Dr. George Rogers Mansfield, a former geologist at the United States Geological Survey. Mandfieldite is an uncommon mineral that occurs of hydrothermal origin in altered and mineralized andesitic pyroclastic rocks at its type locality at Hobbart Butte in Oregon, USA. Other localities for Mansfieldite include in Mexico, Germany, France, England, Algeria, Australia, and Kazakhstan.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/mansfieldite.pdf

Mapimite

Named for the type locality at Mina Ojuela in Mapimi, Durango, Mexico. Mapimite is a rare mineral that occurs only at its type locality and a newer locality in Greece and is found in oxidized arsenic-bearing polymetallic ore deposits of hydrothermal origin. Associated minerals include scorodite, adamite, smithsonite, and limonite.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/mapimite.pdf

Marcasite

Name is of Arabic or Moorish origin and was applied to pyrite and other minerals of similar color and/or luster. Marcasite is a common mineral and is widespread with thousands of localities worldwide. It occurs under highly acidic, but low temperature conditions in sedimentary and hydrothermal environments.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/marcasite.pdf

Marecottite

Occurs in weathered hydrothermal breccia veins at the contact between the pre-Variscan gneissic basement of the Aiguilles Rouges massif and the carbobiferous Vallorcine granite.

It is associated with gypsum, uraninite and secondary uranyl sulfates such as rabejacite, johannite and ktenasite at the type locality. Marecottite forms very brittle, elongated, diamond shaped platelets forming rosettes, is yellow-orange and is reported to be nonfluorescent at the type locality. It is a member of the Zippeite group with extensive solid solution in members rich in Mg, Ni, Ca, Fe, Mn, Zn. At the Rožná deposit in Moravia, Czech Republic, Marecottite occurs with Natrozippeite (fluorescent). Optically, it is biaxial with indices of refraction between 1.735 to 1.750 measured in the (011) face and fair pleochroism.

Originally found at La Creusaz uranium prospect near the village of Les Marécottes, Trient Valley, Valais in the Alps of Switzerland.

For more information see http://rruff.info/rruff_1.0/uploads/CM42_215.pdf .,
Also Roth, Philippe (year?), Minerals first discovered in Switzerland pg 106. An excellent photo here along with an SEM image.

Margaritasite

Named for the co-type localities of the mineral at the Margaritas No. 1 and Margaritas No. 2 mines in Chihuahua, Mexico. The Margaritas mines are the only locality for Margaritasite and it occurs there as filling pores and casts of phenocrysts in felsic volcanic tuffs that have been altered by hot hydrothermal fluids. Margaritasite is strongly radioactive.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/margaritasite.pdf

Margarite

Phyllosilicate - Monoclinic - Mica group member. Brittle - Dioctahedral. Al occupying the (M) octahedral positions with sub's of Lithium, Ca (or possibly Na) at the Interlayer spots, and hydroxyl at the (A) positions. Be and Al can replace Si at the (T) positions. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.

Rarely as good pseudohex. crystals, usually scaly or platy aggregates. Grayish pink to pink, but also yellowish. Occurs mainly with diaspore in contact metamorphic deposits (Bernard & Hrysl), also in chlorite schists (Mindat). Associated with corundum, diaspore, tourmaline, staurolite, glauphane, chlorite, and magnetite...in high aluminun deposits (Handbook of Min.).

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