Milarite Value, Price, and Jewelry Information

Milarite: Tsumeb, Namibia (0.53 cts). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Milarite

Very rare milarite crystals can occur in green and yellow colors. Transparent material can yield small but pleasant looking faceted gems for collectors.

Milarite Information

Data Value
Name Milarite
Crystallography Hexagonal. Crystals prismatic and tabular; in grains.
Refractive Index 1.529-1.551
Colors Colorless, white, pale green, yellowish, yellowish green.
Hardness 5.5-6
Fracture Conchoidal to uneven
Birefringence 0.003
Cleavage None
Luminescence Some specimens may fluoresce and phosphoresce under SW and LW UV. (See “Identifying Characteristics” below).
Luminescence Present Yes
Absorption Spectrum Not diagnostic
Formula K2Ca4Be4Al2Si24O60·H2O
Optics = 1.532-1.551; e = 1.529-1-548. Uniaxial (-).
Optic Sign Uniaxial -
Luminescence Type Fluorescent, Phosphorescent, UV-Long, UV-Short
Luster Vitreous
Specific Gravity 2.46-2.61
Transparency Transparent to opaque
Pleochroism None
Etymology After the Val Milar, Switzerland, because the mineral was (mistakenly) thought to have occurred there.
Occurrence In vugs in granites and syenites; hydrothermal veins.
Parallel-growth milarite crystals - Namibia

Cluster of parallel-growth milarites, 1.7 x 1.5 x 1.2 cm, Milarite locality, Rossing Mountains Area, Erongo Region, Namibia. © Rob Lavinsky, www.iRocks.com. Used with permission.

Comments

Milarite belongs to the mineral group named after itself. Sometimes called the osumilite group, this group also includes sugilite and other rarely faceted minerals, such as poudretteite and sogdianite.

Identifying Characteristics

Milarite was originally known as a green mineral, until fine yellow crystals were discovered in Mexico in 1968.

Some milarites may luminesce. Shortwave (SW) ultraviolet (UV) light may cause blueish white or greenish white fluorescence and phosphorescence, while longwave (LW) UV light may cause medium chalky green fluorescence and weak phosphorescence.

milarite crystal - Mexico

Yellow-green milarites on white valencianite, milarite crystals up to 0.6 cm across, Valenciana Mine, Guanajuato, Mun. de Guanajuato, Guanajuato, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.

Enhancements

No known gemstone treatments or enhancements.

Sources

Guanajuato, Mexico produces yellow and yellow-green gem-quality crystals on matrix, and some larger Mexican crystals have transparent areas suitable for cutting.

Minas Gerais, Brazil and Tsumeb and the Erongo region in Namibia have also yielded small, facetable material. 

Other notable crystal sources include the following locations:

  • St. Gotthard, Switzerland: green crystals.
  • China; Spain; New Hampshire, United States.
milarite crystal - Spain

Milarite crystal, Venero 1 Quarry, Cadalso de los Vidrios, Madrid, Spain. Photo by Christian Rewitzer. Licensed under CC By-SA 3.0.

Stone Sizes

Crystals can occur up to about 4 cm across, but facetable areas in such crystals are very small. Thus, stones over 1 carat could be considered large for the species.

freeform-cut milarite - Brazil

Freeform-cut milarite, 0.98 cts, 8.9 x 6.1 mm, Minas Gerais, Brazil. © The Gem Trader. Used with permission.

Care

With a hardness of 5.5 to 6 and no cleavage, milarites could make suitable jewelry stones if worn with protective settings. However, you’re more likely to find them — if at all — in mineral collections than jewelry collections.

Stay on the safe side and refrain from cleaning these rare gems in mechanical systems. Instead, use a soft brush, mild detergent, and warm water. Consult our gemstone jewelry care guide for more recommendations.

Milarite rough and cut set (crystal: 1.4 x 1.3 x 1.3 cm; emerald-cut gem: 1.38 cts; ), Jaguaracu, Minas Gerais, Brazil. © Rob Lavinsky, www.iRocks.com. Used with permission.

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