Bytownite: One of the Rarest Gemstones
Bytownites are not usually known in the gemstone industry because its composition and occurrence are somewhat hard to find. It had become one of the rarest gemstones belonging to the plagioclase feldspars family.
One of the rarest gemstones to be the fifth member of the plagioclase family is the bytownite. Its composition comprises of minerals that range from pure albite to anorthite. Bytownite from the real class is defined as at least 90-70% calcium and 10-30% sodium. This should be seen in the position of the structure of its crystal. To identify feldspars, one should look into the gradations of density and refraction when chemical analysis or optical measurements are absent.
Plagioclase feldspars show a type of twinning named after pure albite. Twinning is formed when a stack of layers twin together which are fractions of several millimeters thick. The formation of bytownite exhibits a grey to white crystal that shows striations.
Bytownite has two properties namely the refractive indices and specific gravity .Its specific gravity varies between 2.75-2.76. To precisely determine these properties will enable you to identify and analyze the mineral. It should be determined together with diffraction, chemicals, and petrographic analysis.
Metamorphic complexes and intrusions occur in bytownite.
The Mineral's History and Origin
Bytownite's name was derived from Bytown (now known as Ottawa in Canada) by T. Thomson who found it in a boulder near the area. T. Thomson was also the person who gave the name to this stone who later found out that this material is a mixture when looked under the microscope. This happened in 1835.
G. Tschermak was the person who 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.
Characteristics or Properties
Bytownite's hardness ranges from 5.5-6.0 that's why aside from being rare, it is also quite fragile. The specific gravity is 2.75. Color would normally be a wide variety of gray hues, white, and pale yellow. Others can exhibit colorless properties. Its chemical composition can be traced as calcium sodium aluminum silicate. Its fracture would be conchoidal. The luster is glassy-like; if weathered will perform vitreous to translucence.
Habits in crystals will be tabular or blocky. Free crystals are rarely seen. Although a square or rectangular cross-section is perforated together with pinacoid terminations and a slanted dome. Twinning is a general attributein plagioclases. Bytownite is found as small grains in compact masses and gabbros.
A bytownite's cleavage is immaculately perfect wherein they form prisms of the right angle. It has a white streak and is associated with minerals like pyroxenes, biotite and hornblende.
Other significant characteristic is that the striations that appear can cause a simple grooved effect on cleavage surfaces. Refraction is approximately 1.575 to 1.585.
Occurrences, aside from Canada, are also found in South Africa and Scotland.
To indicate this mineral, you should identify its striations, occurrence, index of refraction and density.
Bytownites must be cleaned with warm water and polished with a clear, dry cloth. Refrain from using harsh chemicals to avoid destroying the integrity of the stone.