Humite Value, Price, and Jewelry Information

Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons

Humite

Humite Information

Data Value
Name Humite
Colors Slightly brownish yellow, yellow, deep orange
Crystallography Varies by group member. See "Identifying Characteristics" below.
Refractive Index Varies by group member, 1.563-1.674. See "Identifying Characteristics" below.
Luster Vitreous.
Hardness 6 - 6.5
Fracture Subconchoidal, uneven
Specific Gravity 3.15-3.35. See table below.
Birefringence Varies by group member, 0.026-0.041. See "Identifying Characteristics" below.
Cleavage Poor
Stone Sizes Cut humites are always small, generally in the l-3 carat range. Crystals tend to be dark and filled with inclusions and fractures. Larger cut gems would be extremely rare.
Luminescence Usually inert in SW, sometimes golden yellow; dull orange to brownish orange in LW.
Luminescence Present Yes
Luminescence Type Fluorescent, UV-Long, UV-Short
Transparency Translucent to transparent.
Pleochroism

See “Identifying Characteristics” below.
Optics

Biaxial +. See “Identifying Characteristics” below.
Optic Sign Biaxial +

Comments

Faceted chondrodite is almost unknown, a pity since the color is very rich and the material is hard and durable enough for wear. Cutting presents no great difficulty, but rough is virtually unobtainable, and only tiny stones could be produced. The same is true for norbergite and humite. The exception seems to be clinohumite from the Pamir Mountains in the USSR. Crystals occur there in sizes allowing the production of small (1-3 carats), slightly brownish yellow but flawless gems. This material fluoresces slightly orangy yellow in SW. Only a handful of gems have been cut.

Members of the Humite group include Humite, Clinohumite, Norbergite, and Chondrobite.

These minerals are easily confused with each other as they have similar properties. The compositions are related in a very distinctive way:

  • Norbergite:        Mg(OH,F)2 · Mg2(SiO4)
  • Chondrodite:     Mg(OH,F)2 · 2Mg2(SiO4)
  • Humite:                Mg(OH,F)2· 3Mg2(SiO4)
  • Clinohumite:      Mg(OH,F)2· 4Mg2(SiO4)
  • TiO2 present in humite and clinohumite strongly affects their optical properties. All members of this group have poor cleavage and vitreous luster. All are biaxial (+) and generally yellowish brown in color.

Names

Chondrodite from the Greek chondros, a grain, in allusion to the mineral’s granular nature. Humite is named after Sir Abraham Hume, an English collector of gems and minerals of the nineteenth century. Norbergite is named after the locality at Norberg, Sweden, where it is found. Clinohumite is the monoclinic end of the humite-clinohumite series.

Occurrence

In contact zones in limestone or dolomite. Rarely in alkaline rocks of igneous origin. This paragenesis is true for all members of the humite group.

  • Wiberforce, Ontario, Canada.
  • Tilly Foster Mine, Brewster, New York: fine crystals of chondrodite, reddish brown, some rather gemmy, associated with humite and Clinohumite This locality is the source of most gem chondrodite.
  • Kafveltorp, Orebro, Sweden: yellowish material. Pargas, Finland: yellowish material. Loolekop, East Transvaal: in a carbonatite .
  • Norbergite from: Franklin, New Jersey; Orange County, New York; Norberg, Sweden.
  • Clinohumite from California: Ala, Italy: Malaga. Spain: Lake Baikal, USSR.

Norbergite

Chondrodite

Humite

Clinohumite

 USSR
Crystollagraphy orthorhombic monoclinic orthorhombic monoclinic
Colors yellowish tan yellow, brown, red yellow, deep orange yellow, brown, white
Hardness 6.5 6.5 6 6
Density 3.15-3.18 3.16-3.26 3.20-3.32 3.17-3.35
Optics
α 1.563-1.567 1.592-1.615 1.607-1.643 1.629-1.638 1.631
β 1.567-1.579 1.602-1.627 1.639-1.675 1.662-1.643 1.639-1.647
γ 1.590-1.593 1.621-1.646 1.639-1.675 1.662-1.674 1.668
2V 44-50° 71-85° 65-84° 73-76°
Birefringence 0.026-0.027 0.028-0.034 0.029-0.031 0.028-0.041 0.037
Pleochroism
α pale yellow very pale yellow/brownish yellow yellow golden yellow/ deep reddish yellow
β very pale yellow colorless/ yellowish green colorless/ pale yellow pale yellow/orange yellow
γ colorless colorless/pale green colorless/ pale yellow pale yellow/orange yellow

 

by Joel E. Arem, Ph.D., FGA