| View Cart ⇗ | Info

“The mineral corundum which includes the precious stones ruby, sapphire, and topaz, contains alumina, or aluminum oxide, Al2O3. It is found in nature crystallized in rhombohedral forms, having a specific gravity of 3.9, and is scarcely inferior in hardness to diamond.” —Hallock 1905


V. I. Hallock I.C.S. Refrence Library (Scranton: International Textbook Company, 1905) 11:60


TIFF (full resolution)

2281×2400, 487.0 KiB

Large GIF

973×1024, 72.9 KiB

Medium GIF

608×640, 40.5 KiB

Small GIF

304×320, 16.0 KiB