Carbonado typical gem diamonds. Lead isotope analyses have been interpreted as documenting crystallization of carbonados about 3 billion years ago. The carbonados are found in younger sedimentary rocks. Mineral grains included within diamonds have been studied extensively for clues to diamond origin. Some typical diamonds contain inclusions of common mantle minerals such as pyrope and forsterite, but such mantle minerals have not been observed in carbonado. In contrast, some carbonados do contain inclusions of minerals characteristic of the Earth's crust: these inclusions do not necessarily establish formation of the diamonds in the crust, however, because while these obvious crystal inclusions occur
What Is Art? in Tolstoy and his problems: essays. London: Grant Richards. pp. 66–101. Maude, Aylmer (1901b). “"What is Art?" - Tolstoy’s Theory of Art”, in Tolstoy and his problems: essays. London: Grant Richards. pp. 102–127. Noyes, George (1918). Tolstoy. London: Duffield. Pevear, Richard (1995). "Preface" in Tolstoy, Leo (1995 [1897]). "What is Art?" (Translated by Richard Pevear and Larissa Volokhonsky). London: Penguin. Simmons, Ernest (1973). "What is Art?", in Tolstoy. London: Routledge and Kegan Paul. pp. 175–189. What Is Art? What is Art? ( "Chto takoye iskusstvo?") is a book by Leo Tolstoy. It was completed in Russian in 1897 but first