Mineral description : Piemontite

Piemontite on feldspar from Berghamn, Sweden.
Specimen size 4x10 cm.
Close up of piemontite on feldspar from Berghamn, Sweden.
Crystal group app. 8 mm in diameter.
Piemontite on quartz from Ultevis, Sweden.
Calcite on the lower part. Specimen size 25x9x5 cm.
Close up of piemontite on quartz from Ultevis, Sweden.
Picture area approximately 8x6 cm.

Mineral class Silicates : Sorosilicates : Epidote - Vesuvian group
Chemical formula Ca2(Al,Mn3+,Fe3+)3(SiO4)(Si2O7)O(OH)
Crystal system Monoclinic
Habitus Prismatic bladed or acicular crystals up to 8 cm, commonly in grainy or massive aggregates.
Cleavage Perfect in {001}, poor in {100}. Brittle, uneven fracture.
Hardness 6 - 6.5
Density 3.46 - 3.54
Color Deep reddish brown, red, purple to almost black.
Streak Reddish
Luster Vitreous, translucent to opaque.
Description Piemontite is a mineral closely related to epidote which it forms a substitution serie with. Since the formation of piemontite is dependant of a high concentration of manganese it is commonly found together with other manganese minerals.
Occurance In metamorphosed rocks, in manganese deposits and in low temperature hydrothermal veins.
Associates Epidote, tremolite, quartz, calcite, feldspar and other manganeese minerals.
Notes The Mn content should be at least 5% before it is called piemintite.
Klinozoisite and red colored epidote is easily mistaken for piemontite.
Localities A not so common mineral in Scandinavia but with a few good localities.

Sweden :

  • Berghamn, Nordingrå. Nice radiating aggregates of crystals in calcite filled fractures.
  • Ultevis. As large massive banded aggregates in bedrock and single crystals up to a couple of centimeters in size.
  • Garpenberg Norra, Dalarna. As red banded massive aggregates.
  • Långban, Värmland. With yellow garnet, manganophyll and schefferite. Not common.
  • Jacobsberg, Nordmark, Värmland. As large massive aggregates.

Norway :

  • Vestpolltind iron manganese deposit, Hinnøy, Lofoten.
  • Brandsnuten manganese deposit.

Finland : (Sorry if the names are messed up, but I don't speak Finnish)

  • Kiihtelysvaara, Raatevaara. In carbonatic quartzite.
References 
  John W. Anthony et. al. 1995, Handbook of mineralogy,
     Volume II part 2
     Pg. 648
  Hedin, L. H. 1985, Mineral i Sverige,
     Bonnier Fakta
     Pg. 149
  Henrich Neumann 1985, Norges Mineraler,
     Norges Geologiske Unders⊝kelse, Skrifter 68
     Pg. 165-166
  Kai Hytönen 1999, Suomen Mineraalit
     Gummerus Kirjapaino Oy, ISBN 951-690-745-8
     Pg. 249-250

To silicate index.
Mineral group index.
Main index.

If you have some questions, suggestions or comments you are welcome to write me a line or two.

axelsson@acc.umu.se
To my homepage.
Last changed : 2004-02-24