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Bytownite: A Rare Gemstone

Bytownite is not a well known gemstone and most probably you may not be familiar with gemstone name. It is because composition and occurrence of bytownite is not very common and is hard to find. It is one of rarest gemstones minerals belonging to the plagioclase feldspars family.

Bytownite Introduction

It is one of rarest gemstones to be the fifth member of the plagioclase family is the bytownite. Its composition ranges between pure albite and anorthite. Bytownite contains 90-70% calcium and 10-30% sodium in its composition. Feldspars, can be identified because of gradations of density and refraction when chemical analysis or optical measurements are not available.

Albite twining its commonly observed in Plagioclase feldspars. This kind of twinning is formed when a stack of layers twin together which are just few millimeters thick. The bytownite mineral exhibits a grey to white crystal that shows striations.

Bytownite gemstone has two properties namely the refractive indices and specific gravity on basis of which it can be easily identified .Its specific gravity range between 2.75-2.76. The refractive index of bytownite is 1.563 – 1.572.  To precisely determine these properties will enable you to identify and analyze the mineral. It should be determined together with diffraction, chemicals, and think section analysis in petrography microscope.

Metamorphic complexes and intrusions also occur in bytownite.

The Mineral’s History and Origin

Bytownite’s name was taken from Bytown (now known as Ottawa in Canada) by T. Thomson who encountered this mineral in boulder near the Bytown. In 1835 T. Thomson gave the name to this stone and later he found out that this material is a mixture when looked under the microscope.

G. Tschermak applied the name to whatever mineral that lies between anorthite and labradorite. The petrologists adopt this, in the modern time.

How Bytownite Became Rare

Bytownite is not usually found around obvious places. It normally occurs in tiny grains found in igneous rocks which are said to be lime-rich. The clear yellow crystals are usually found in Oregon and Mexico.

Properties of Bytownite

Bytownite’s is not quite hard gemstone and its hardness ranges from 5.5-6.0 that’s why aside from being rare, it is also quite fragile. The specific gravity of Bytownite is 2.75. It comes in wide variety of  gray hues, white, and pale yellow. Colorless variety also exists in Bytownite stone. Chemically it is calcium sodium aluminum silicate. Its fracture would be conchoidal. It has vitreous lusture; if weathered will perform vitreous to translucence.

Bytownite gemstone shows tabular or blocky crystall habit. Free crystals are extremely rare. Although a square or rectangular cross-section is perforated together with pinacoid terminations and a slanted dome. Twinning which is characteristic property of plagioclase family is founf in Bytownite mineral. It is also is found as small grains in compact masses and gabbros.

Bytownite shows immaculately perfect cleavage wherein they form prisms of the right angle. Its streak and is associated with minerals like pyroxenes, biotite and hornblende.

Other significant properties include striations that creates a simple grooved effect on cleavage surfaces. Refractive index of Bytownite is 1.575 to 1.585 on refractometer. It can be easily identified by  its striations, occurrence, index of refraction and density.

Occurence of Bytownite

Canada is main source of Bytownite and named for its occurrence at Bytown (now Ottawa), Canada. Other noted occurrences in Canada are Shawmere anorthosite in Foleyet Township, Ontario, and on Yamaska Mountain, near Abbotsford, Quebec. In the United states Bytownite mineral is found in the Stillwater igneous complex of Montana; from near Lakeview, Lake County, Oregon. It also occurs in the Lucky Cuss mine, Tombstone, Arizona; and from the Grants district, McKinley County, New Mexico. In the eastern US, it occurs at Cornwall, Lebanon County, Pennsylvania and Phoenixville, Chester County, Pennsylvania.

Worldwide it is present is occurs on Rùm island, Scotland, Cumberland, England and Eycott Hill, near Keswick,. It is also reported from Naaraodal, Norway and in the Bushveld igneous complex ( famous for large layered igneous intrusion) of South Africa. It is also found in Isa Valley, Western Australia.

Gemstone Care

Bytownites must be only be cleaned with warm water and polished with a clear, dry cloth. It is sensitive mineral so one should avoid using harsh chemicals to protect the integrity of the stone.

By | 2018-03-06T08:30:26+00:00 March 6th, 2018|Categories: Gemology, Gemstones|Tags: , , , |0 Comments

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