Thus, corundum when pure is colourless, but the presence of traces of certain mineral substances imparts to it not only the red of ruby and the blue of sapphire, but almost every other colour.
From his experiments he believes that yellow corundum, or oriental topaz, may have been formed from blue corundum under the influence of radioactive substances present in the soil in which the sapphire was embedded.
Besides these there may be corundum and carbide of silicon, arising from impurities in the materials employed.
This dust or powder, consisting of corundum or zircon, might have been found without any great difficulty by the men of the Stone Age.
Corundum is a sesquioxide of aluminum, with the percentages aluminum 53.
The mineral species Corundum affords a number of gems known by different names.
Thus red Corundum is known as the ruby and blue Corundum as the sapphire.
The Spinel ruby seems to have been known to the ancients equally with the corundum ruby, and the two were probably often confounded.
Of the different colors of Corundumabove referred to, the blue or sapphire is most common, the red or ruby next.
This high specific gravity affords an easy means of distinguishing the gems of Corundum from those of other species.
Blue Corundum exhibits various shades from light to dark, the color most highly prized being that known as cornflower blue.
It is thus neither as hard nor as heavy as corundum ruby.
In our own country ruby Corundum is occasionally found in connection with opaque Corundum in Macon County, North Carolina.
Not only is Spinel ruby related tocorundum ruby in color and use, but the two are frequently associated together in nature.
The most ancient method consisted, in obtaining a flat surface by rubbing or scraping, with corundum or other hard and wearing stone, the stone to be engraved.
Pliny says, corundum was used in the form of a splinter fixed in an iron style.
Chaper found diamond with corundum in a decomposed red pegmatite vein in gneiss.
The mineral occurs as an alteration product of corundum or emery, and is found in granular limestone and other crystalline rocks.
The surfaces of crystals of corundumare often clouded or dull, whilst its classification of lustre is vitreous.
The emery or corundum wheel is then put on the arbor and tried for being in balance.
Corundum is a mineral similar to emery, and corundum wheels are made and used in the same manner as emery wheels.
At the top of F are two slide rests A A, one on each end, carrying emery or corundum wheels W, and the roll R, which rests in the bearings B, rotates between these emery wheels.
This greater density, be it noted, occurs from the difficulty in mixing the corundum or other abrasive grains with the cementing material with entire uniformity throughout the mass.
Corundum is characterised by a high specific gravity (4.
Corundum cannot be powdered in Wedgwood, or even agate, mortars; since it rapidly wears these away and becomes contaminated with their powder.
If the substance is insoluble in hydrochloric acid it is finely powdered and fused with "fusion mixture" with the help, in the case of corundum (which is very refractory) of a little caustic soda or potash.
McTeague turned, one foot on the pedal of his dental engine, the corundum disk whirling between his fingers.
The corundumburr in McTeague's engine hummed in a prolonged monotone.
When my companions washed the sands of likely stretches of river beach for fine gold, I examined the waste for corundum crystals, but I found no signs of them.
I carried the specimen of corundum in my waistcoat pocket.
Accordingly corundum, adamantine spar, and the zircon, or hyacinth, baffled his attempts for a considerable time, and induced him to consider the earth of corundum as of a peculiar nature.
His analysis of corundum and sapphire, and his observations on the affinity between magnesia and silica, are valuable, and led to considerable improvements in the method of analysis.
Important deposits of corundum were discovered in Asia Minor by J.
In these cells the pulverized enamel is laid and then fused; afterwards it is filed with a corundum file, then smoothed with a pumice stone and polished by means of crocus powder and rouge.
The proportion of corundum in this emery is said to vary from 37 to 57%.
The hardness of emery is about 8, whereas that of pure corundum is 9.
Of the corundum gems (sapphire, ruby, and other colored varieties), no sapphires of fine blue color and no rubies of fine red color have been found.
The term corundum is often restricted to the remaining kinds, i.
Corundum is used largely for watch-jewels, and for bearings in electrical apparatus.
See Joseph Hyde Pratt, "Corundum and its Occurrence and Distribution in the United States," Bulletin U.
Corundum occurs also at many localities in Montana, where the crystals are often of gem quality.
Corundum occurs also in Canada in an igneous rock, a nepheline-syenite, associated with Laurentian gneiss.
Large deposits of corundum exist in the United States, especially in N.
Next to diamond, corundum is the hardest known mineral.
Other crystals show a tabular habit, consisting usually of the basal pinacoid with a rhombohedron, and it is notable that this habit is said to be characteristic of corundum which has consolidated from a fused magma.
Important deposits were discovered by the Geological Survey in 1896, in Hastings county, Ontario; and corundum is now worked there and in Renfrew county.
Coarse dull corundum is found in many localities, and usually has higher commercial value as an abrasive agent than emery, which is less pure.
The mineral has been extensively worked, as at Corundum Hill, Macon county, N.
Corundum has no true cleavage, but presents parting planes due to the structure of the crystal, which have been studied by Prof.
Corundum is the hardest substance known, next to the diamond.
Corundum is found in feldspar veins, and associated with chlorites in serpentine rock.
The natural varieties, corundum and emery, are used for cutting and grinding purposes; the purest forms, together with the artificially prepared oxide, are largely used in the preparation of aluminium.
This is true whether it has reference to a grindstone, emery, corundum wheel, or a plain oil stone.
As the wheel is of emery, corundum or other quickly cutting material, and is always run at a high rate of speed, a great heat is evolved, which is materially increased by pressure.
The domestic production of emery is mainly from New York and Virginia, and corundum comes from North Carolina.
Corundum is a product of contact metamorphism and also a result of direct crystallization from molten magma.
Emery and corundum are used in various forms for the grinding and polishing of hard materials--steel, glass, stone, etc.
Canadian corundum occurs as a constituent of syenite and nepheline-syenite in Lower Ontario.
In North Carolina and Georgia, the corundumoccurs in vein-like bodies at the contact of peridotite with gneisses and schists, and also in part in the peridotite itself.
Production of corundum has come from Canada, South Africa, Madagascar, and India.
Corundum as an abrasive is the mineral of this name--made up of anhydrous aluminum oxide.
Silex Corundum appeared to understand, and he indicated that the unfortunate man would receive attention.
Silex Corundum made a motion as of some body flying through space, and looked inquiringly at the travelers.
And I should not be surprised if corundum could be found in those rocks back of the house.
The color of corundumis usually brown, but it varies greatly.
Emery is a fine-grained mixture of corundumand other minerals, especially magnetite.
No jeweler can afford to risk his reputation for knowledge and for integrity by selling as a natural stone any gem which does not possess the minor defects common to practically all corundum gems.
The yellowcorundum rarely has a color that is at all distinctive.
Similarly the corundum gems (ruby and sapphire), being even harder than true topaz, take a splendid surface finish and have a very keen vitreous luster.
The best practice with regard to naming the corundum gems is to call the red material, when of a good, full red of pleasing shade, ruby.
Thus every diamond consists mainly of pure carbon, and all the corundum gems (ruby and the various colors of sapphire) consist mainly of pure oxide of aluminum.
Thus, instead of having a whole series of specific gravities to remember one has only to remember that all the corundum gems have a specific gravity of approximately 4.
It is easily seen that if one recognizes the similar nature of all the many colors and shades of corundum that the number of things that one has to remember in order to be well acquainted with these stones is considerably diminished.
The red of the rubellite should not deceive anyone who has ever seen a fine corundum ruby.
The yellow corundum is also sometimes called "King topaz," especially in Ceylon.
Perhaps the most common of the defects of natural corundum gems is the peculiar appearance known as "silk.
It gives one of the best accounts to be had of the history of the artificial production of precious stones, especially of the corundum gems.
As was said under ruby, nothing but red corundum should receive that title.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "corundum" in a variety of sentences. We hope that you will now be able to make sentences using this word.
