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Mineralpedia Details for Jahnsite-(CaMnMg)

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Jahnsite-(CaMnMg)

Jahnsite-(CaMnMg)

Named for Richard H. Jahns (1915-1983). Occur predominately in zoned pegmatites. At the type locality, the Tip Top mine near Custer South Dakota, crystals occur as light to dark brown, deep red-brown and red-orange, vitreous, short to long prismatic crystals to 7mm. Crystals are striated length-wise on the prism face [010] and are typically tabular and found as singles and subparallel groups in altered Triphylite matrix with Leucophosphite, Rockbridgeite, Hureaulite and Tavorite. Jahnsite (CaMnMg) has not been found in association with Jahnsite (NaFeMg), which occurs in Heterosite matrix.

For best reference see unpublished Thomas Campbell MS thesis, SDSM&T 1984.

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

Formula
CaMn2+Mg2Fe3+2(PO4)4(OH)2ยท8H2
Crystal System
Monoclinic 
Cleavage
Good, None, None 
Luster
Vitreous - Adamantine 
Color
brown, purplish brown, yellow, yellow orange, greenish yellow 
Streak
white 
Class
Monoclinic - Prismatic 
Fracture
Brittle 
Hardness
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Jahnsite-(CaMnMg) from Tip Top mine, Custer Co., South Dakota, United States

Jahnsite-(CaMnMg)
            from Tip Top mine, Custer Co., South Dakota, United States
Special Info
Type Locality

Nut brown, striated, tabular Jahnsite (CaMnMg) to 2mm.

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