Moreover these defects are characteristic of the corundum gems.
To polish diamonds they make use of the powder of adamantine spar, or the corundum stone.
The surfaces of crystals of corundum are often clouded or dull, whilst its classification of lustre is vitreous.
The stones have been rubbed into shape apparently by corundum.
It is interesting to note that the corundum gems undergo marked change in color under the influence of radium.
corundum is the hardest substance known, next to the diamond.
It is ranked 10 in the scale of hardness on which minerals are classified, corundum being the next below it.
The proportion of corundum in this emery is said to vary from 37 to 57%.
corundum is characterised by a high specific gravity (4.0) and extreme hardness.
Well, the sapphire in all its beautiful tints is only a variety of corundum, colored by metallic oxide.
"very hard mineral," 1728, from Anglo-Indian, from Tamil kurundam "ruby sapphire" (Sanskrit kuruvinda), of unknown origin.
An extremely hard mineral occurring in many colors, either as shapeless grains or as rhombohedral crystals. It also occurs in gem varieties such as ruby and sapphire and in a dark-colored variety that is used for polishing and scraping. Corundum is found in igneous and carbonate rocks. Chemical formula: Al2O3.