This kind of twinning is especially frequent in crystals of spinel, and is consequently often referred to as the "spinel twin-law.
Examples of simple forms amongst crystallized substances are octahedra of alum and spinel and cubes of salt and fluorspar.
The spinel and ruby occur together in nature, stones from Burma being as often spinel as true Oriental ruby.
In this case, when these impurities have accumulated to a certain point they unite with the alumina, andspinel then separates, as it crystallizes more easily than ruby.
Ebelmen produced the white sapphire and rose-coloured spinel by fusing the constituents at a high temperature in boracic acid.
In the artificial production of the ruby it sometimes happens that spinel crystallizes out when true Oriental ruby is expected.
Then follows the topaz, which, withspinel and chrysoberyl, has a hardness of 8; whilst quartz falls a degree lower.
The fine specimens of spinelruby are worth rather more than half as much as the diamond.
Defn: An igneous rock consisting largely of chrysolite, with pyroxene and picotite (a variety of spinel containing chromium).
An igneous rock consisting largely of chrysolite, with pyroxene and picotite (a variety of spinel containing chromium).
The Moors bring them out of that country to all parts; that is to say, the good and picked ones, cut or uncut, they clean and work them in Calicut, and they are sold for the prices of spinel rubies.
The natives of India call the Spinel the pomegranate ruby and believe to this day that it possesses valuable medicinal properties.
Not only is Spinel ruby related to corundum ruby in color and use, but the two are frequently associated together in nature.
Spinel is thus known among gems chiefly as a relative of the ruby, and this sort of Spinel will first be considered.
The gem gravels of Ceylon, Siam, Australia and Brazil contain both kinds of rubies, and the ruby mines of Upper Burmah, where the corundum ruby occurs in a crystalline limestone, produce also large quantities of Spinel rubies.
Spinel occurs in many other colors besides red, such as orange, green, blue and indigo, as well as white and black.
The Spinel employed as a gem is almost wholly confined to the magnesium aluminate, having the percentage composition alumina 71.
The hardness of Spinel is 8, or about that of topaz, and the specific gravity 3.
The group of Spinel includes in mineralogy a number of species of different though analogous composition.
The localities above mentioned furnish nearly all the Spinel rubies of commerce.
The rough material persists in turbulent mountain streams where weaker minerals are ground to powder, and when cut and polished, spinel will wear well in any jewel.
Such red spinels should be called "Ruby spinel" (and not spinel ruby).
Thus spinel is of about the same hardness as topaz and hence is usually rated as 8 in hardness.
Spinel (which is also rated as 8 in hardness) is really a bit harder than topaz.
Ruby and sapphire are scratched by diamond alone, while chrysoberyl, topaz and spinel scratch all the remaining stones, although they do themselves yield to the scratch of ruby and sapphire.
It is doubly refractive, whereas spinel and the diamond, which two it closely resembles, are singly refractive.
The third and still more remarkable case is that of a spinel from Amity, New York, containing calcite in its crevices, including a perfect canal system preserved in malacolite.
The limestone may have been originally a mass of fragments of this kind with the aluminous and magnesian material of the spinel in their interstices.
On account of their resemblance to the twins of the mineral spinel (which crystallizes in octahedra) these are known as "spinel twins.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "spinel" in a variety of sentences. We hope that you will now be able to make sentences using this word. Other words: alabaster; asphalt; diamond; emerald; jade; mineral; ruby; sapphire; stone
