AGATE

siliceous mineral, being variegated chalcedony, occurring in rounded nodules, which are formed in cavities of igneous rocks by the deposition of silica in layers from percolating water. Iron or other oxides may produce red, brown, and other tints. On account of its hardne and the high polish it can take on, a. has been used as an ornamental stone, and for laboratory appliances, such as mortars and pestles and knife edges for delicate balances. The colors of articles for sale are frequently artificially produced.