File:Sapphires from fluvial gravel (Spokane Sapphire Mine, Montana, USA) 2.jpg

English: (public display, Spokane Sapphire Mine, Montana, USA)

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These sapphire crystals are from a Pleistocene-aged river terrace gravel deposit along the Missouri River in Montana. Small sapphires can be collected from density concentrates (e.g., I collected a 2.09 carat sapphire). Occasional pyrite crystals are sometimes found, such as the pyrite cubes and pyritohedrons. Pyritized fossils are also found occasionally, such as ammonites and brachiopods.

The common color of sapphires from here is extremely pale blue - these samples include dirty yellowish to pale blue to dark blue to pale green to dirty purplish to orangish. The provenance of these crystals may be sapphire-bearing, vesicular, porphyritic andesite dikes.

Sapphires are a variety of corundum, a hard aluminum oxide mineral (Al2O3). Sapphire and corundum have a hardness of 9 on the Mohs Scale. They form hexagonal crystals, have a nonmetallic luster, no cleavage, a white streak, and are relatively heavy for their size.

Locality: derived from a small quarry at the Spokane Gravel Bar, southern slopes of the Missouri River Valley, northeast of the town of Helena, southeastern Lewis and Clark County, western Montana, USA (46° 39’ 40.74” North latitude, 111° 48’ 37.49” West longitude)