Danburite
By Bob Farrar
For the February meeting, the Mineral of the Month will be danburite. Named for Danbury, Connecticut, danburite is a mineral that is popular among collectors, due in part to its often well-formed crystals.
Danburite consists of calcium borosilicate, CaB2Si2O8. It crystallizes on the orthorhombic system. Crystals are typically elongate-prismatic, and may resemble topaz. Topaz, however, has a much more pronounced cleavage. Danburite is usually colorless, but may also be gray, brown, pink, or yellowish. It is a hard mineral, with a hardness of 7 on the Mohs scale. Other physical properties include a specific gravity of 3.0 and a glassy luster. Crystal form and lack of good cleavage are usually sufficient to distinguish danburite.
Danburite occurs in a variety of geological environments. Most commonly, it is found in high temperature contact metamorphic formations and ore veins, but it may also be found in pegmatites and evaporite deposits. The original locality in Danbury, CT, was in a contact zone between marbles and dolomite with granite. That locality is now lost, but danburite occurs at a similar locality in St. Lawrence Co., New York. In recent years, the world's most prolific danburite locality has been Charcas, San Luis Potosí, Mexico, where colorless to pinkish crystals up to several centimeters long are found with datolite, apophyllite, and various ore minerals. Crystals up to 50 cm. have been found at Dalnegorsk, Russia. Golden-brown crystals up to 10 cm occur at the Little Three Mine, a pegmatite deposit, in San Diego Co., CA. Double-terminated gray crystals occur in evaporite deposits in Bolivia. Gemmy danburite is found in alluvial deposits in Mogok, Burma. Other notable localities include Madagascar, Nepal, and Japan.
Danburite is of little economic importance, except as a collector's mineral. Transparent material is sometimes cut into gemstones, but these are mostly for collectors, not the jewelry market. Its often beautiful crystals make it popular with collectors, and it is common enough that most collectors can add it to their collections without having to spend a great deal of money.
Danburite consists of calcium borosilicate, CaB2Si2O8. It crystallizes on the orthorhombic system. Crystals are typically elongate-prismatic, and may resemble topaz. Topaz, however, has a much more pronounced cleavage. Danburite is usually colorless, but may also be gray, brown, pink, or yellowish. It is a hard mineral, with a hardness of 7 on the Mohs scale. Other physical properties include a specific gravity of 3.0 and a glassy luster. Crystal form and lack of good cleavage are usually sufficient to distinguish danburite.
Danburite occurs in a variety of geological environments. Most commonly, it is found in high temperature contact metamorphic formations and ore veins, but it may also be found in pegmatites and evaporite deposits. The original locality in Danbury, CT, was in a contact zone between marbles and dolomite with granite. That locality is now lost, but danburite occurs at a similar locality in St. Lawrence Co., New York. In recent years, the world's most prolific danburite locality has been Charcas, San Luis Potosí, Mexico, where colorless to pinkish crystals up to several centimeters long are found with datolite, apophyllite, and various ore minerals. Crystals up to 50 cm. have been found at Dalnegorsk, Russia. Golden-brown crystals up to 10 cm occur at the Little Three Mine, a pegmatite deposit, in San Diego Co., CA. Double-terminated gray crystals occur in evaporite deposits in Bolivia. Gemmy danburite is found in alluvial deposits in Mogok, Burma. Other notable localities include Madagascar, Nepal, and Japan.
Danburite is of little economic importance, except as a collector's mineral. Transparent material is sometimes cut into gemstones, but these are mostly for collectors, not the jewelry market. Its often beautiful crystals make it popular with collectors, and it is common enough that most collectors can add it to their collections without having to spend a great deal of money.
|
|
|
|