THE MINERAL MILARITE

Milarite is a fairly rare mineral and yet it is one of the two minerals that gives its name to a somewhat large group of silicates, namely the Milarite - Osumilite Group. The group is composed of similar cyclosilicate minerals that are all very rare and very obscure with the exception of milarite, osumilite and sugilite. The primary structural unit of the minerals in the Milarite - Osumilite Group is a most unusual double ring, Si12O30. Normal rings of cyclosilicates are composed of six silicate tetrahedrons; Si6O18. The double rings of the Milarite - Osumilite Group minerals are made of two normal rings linked together by sharing one oxygen in each of the tetrahedrons. The structure is analogous to the dual wheels of a tractor trailer.

Milarite crystals are generally small, but can make excellent micromounted specimens. They are often colored a muted green or yellow and form good prismatic hexagonal crystals. Milarite forms as a primary mineral in granitic pegmatites and syenites, hydrothermal veins and alpine clefts. It has been cut as a gem, but is too rare, small and its general translucency that makes it only suitable to be cut for collectors of rare gemstones. Milarite is named for its locality of first discovery; Val Giuf (Val Milar), Tavetsch, Grischum, Switzerland. Milarite has been known as giufite and giuffite, but milarite is the only accepted name now. Good mineral specimens are available and can be quite attractive, but mostly under magnification.

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white, pale green or yellow.
  • Luster is vitreous to dull.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System is hexagonal; 6/m 2/m 2/m.
  • Crystal Habits include prismatic crystals with a pinacoidal termination.
  • Cleavage is poor in one direction.
  • Fracture is subconchoidal.
  • Hardness is 5.5 - 6
  • Specific Gravity is approximately 2.5 - 2.6 (average)
  • Streak is white.
  • Other Characteristics: Some specimens are fluorescent.
  • Notable Occurrences include the type locality of Val Giuf (Val Milar), Tavetsch, Grischum, Switzerland as well as Jaguaracu, Minas Gerais, Brazil; Valencia Mine, Guananajuato, Mexico; Henneberg, Germany; Kola Peninsula, Russia; Mont Saint-Hilaire, Quebec, Canada; Monte Cervandone, Piemonte, Italy; Langesunsfjord, Norway and Maehren, Czech Republic.
  • Best Field Indicators are hardness, color, luster and locality.
MILARITE specimens:
(hover for more info)
MILARITE specimen mlr-2
$ 38.00
Dims: 3.3 x 3.2 x 1.4" (8.3 x 8.1 x 3.5 cm)
Wt: 4.6 oz. (132 g)
Jaguaracu, Minas Gerais, Brazil
At least 3 small Milarite prisms rest on the crystalline muscovite base of this cabinet piece. The crystals reach maximum dimensions of 5 x 2 mm, though two of them are much smaller than the third. All are in excellent condition, showing no damage, and show good though somewhat warped hexagonal prismatic form. Their color is white and their luster is silky, and they are translucent at best. The muscovite base is in good condition and consists of countless intersecting "books".
no photo
mlr-2 ($ 38.00)
Jaguaracu, Minas Gerais, Brazil
MILARITE specimen mlr-1
$ 50.00
Dims: 1.7 x 1.2 x 0.9" (4.3 x 3.0 x 2.2 cm)
Wt: 1.0 oz. (28 g)
Jaguaracu, Minas Gerais, Brazil
Several stubby, white Milarite crystals rest on the base of this small hand piece. These crystals do not exceed 0.3" (8 mm) in length or 0.1" (3 mm) in diameter but I believe that this size is considered large for crystals of this specie. All have a somewhat warped hexagonal prismatic form, as a hexagonal outline is not very clear, and have a white color and a surprisingly silky luster. Their crystalline base appears to be made up of albite, of the variety known as cleavelandite, due to its strong pseudotrigonal patterning.
no photo
mlr-1 ($ 50.00)
Jaguaracu, Minas Gerais, Brazil
MILARITE specimen mlr-3
$ 30.00
Dims: 2.7 x 1.3 x 0.9" (6.9 x 3.3 x 2.2 cm)
Wt: 1.5 oz. (43 g)
Jaguaracu, Minas Gerais, Brazil
Two complete and two partial Milarite crystals rest on the albite base of this hand specimen. The largest complete crystal has dimensions of 4 x 2 mm, and the other complete one is much smaller. They show a moderately good hexagonal prismatic form; the broken ones show it better, with definable hexagonal cross-sections. All have a white color and a silky luster, and are transparent. The albite base on which they rest is of the variety called cleavelandite, and shows excellent pseudohexagonal blades.
no photo
mlr-3 ($ 30.00)
Jaguaracu, Minas Gerais, Brazil
 

Copyright ©1995-2023 by Amethyst Galleries, Inc.