The white part is from a shining white aluminous schistus, that separates into minute flakes like snow.
"Travels in the Great Desert of Sahara, in the Years of 1845 and 1846"
James Richardson
Where mica abounds, it becomes black and metallic; and the aluminous matter is crystallised in the form of garnets.
"Himalayan Journals V2."
J. D. Hooker
The water has not even any taste, and I can neither offer nor imagine any better explanation, than that it acquires this combustible property by passing over some aluminous land."
"The French in the Heart of America"
John Finley