As of 1998, not a valid term for GeoRef. Use (volcanic glass or glasses) AND (silicates or siliceous composition). For natural glasses which are not volcanic, glass materials is be used. See silicate melts if applicable.
In indexing, use this term only for broad treatments of the entire class of minerals; otherwise, use a narrower term, e.g. orthosilicates, ring silicates, chain silicates, etc.