ONYX MARBLE. A beautiful ornamental stone composed chiefly of carbonate of lime col ored by iron or manganese. This is the commer cial variety of oynx, while true onyx is a banded variety of marble. Commercial onyx marble really includes two rock types, both of which are chemically deposited. The one is a hot-spring deposit or travertine, which is formed on the surface, the other is a cold-water deposit which is formed on the floor, roof, or walls of limestone caves in the same manner as stalagmites and stalactites. Owing to its method of formation, the cave onyx usually occurs in less extensive de posits than the travertine onyx marbles, which have been formed around springs, and both are far less extensive and less regular in their ar rangement than the ordinary bedded limestones or marbles. The beautiful banding seen in onyx is due to the deposition of successive layers of carbonate of lime, while the colored c•londimgs and veinings are caused by metallic oxides, especially iron. The fact that onyx marble is colored along the veins or cracks is not necessarily due to an infiltration of the iron along these lines, but is caused by the iron carbonate in the stone being locally oxidized along the cracks. The cave onyx marbles are more coarsely crystalline and less translucent than the travertine onyx. Onyx marbles, although rarely occurring in large quan tities, are widely distributed. The earliest worked deposits were probably those of Egypt, which were used by the ancients for the manufac ture of ornamental articles and religious ves sels. The Greeks and Romans also valued the material; the deposits near Urinniali and Yezd were extensively worked during the prosperous days of the Persian Empire. Many of the spring
deposits occur in regions of recent volcanic ac tivity and all of the known occurrences are of recent geological age. In the United States onyx marbles are said to occur in Arizona, California, and Colorado, but the American deposits have not been developed commercially to a large ex tent, most of the onyx used in the United States being obtained from Mexico, while small quanti ties are imported from Algeria and Egypt. The Mexiean stone has for years been obtained chiefly from the vicinity of Pueblo and more recently from the vicinity of San Antonio. Mexican ony.e is the name given to banded varieties of aragonite that are found extensively in Arizona, Missouri, and California, as well as in Tveali, Mexico. It is used for decorative purposes. The value of onyx varies considerably, the poorer grades sell ing for as little as 50 cents per cubic foot, while the higher• grades bring $50 or more.
BInuoGrsrnY. DeKalb, ''Onyx Marbles." in Transactions of time Anicrieult Institute of Mining En,gineer•.c (New York, 1890) ; Merrill, Stones for• Building and Decoration (241 ed., New York, 1897) ; The Onyx Marbles. Their Origin, Composition, and Uses, Both Ancient and Mod ern, Annual Report of the United States Nation al .1\I ( Washington, 189d) ; Merril I. "Onyx," in Mineral Industry, vol. ii. (New York, 1894).
00, or UHO. One of the names of the Ifa \val. ian feather-cloak bird. The bird is so called from its cry. See Mono, and Plate of CREEPERS..