The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Specific Gravity||See table below.|
|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.|
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.
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.
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.
|Colors||yellowish tan||yellow, brown, red||yellow, deep orange||yellow, brown, white|
|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|