wood-opal

Century Dictionary and Cyclopedia

1. n. Silicified wood; opalized wood. It is found in great abundance in many parts of the world, but especially in the auriferous gravels of the Sierra Nevada of California, where extensive forests have been exposed by hydraulic mining, in which the trunks of the trees have been converted into amorphous silica, or opal, which usually contains a small percentage of water, although this is not considered as being essential to its composition. Also called xylopal. See fossil wood (under wood), and silicify.