Schorl-rock, a compound of quartz and schorl or black Tourmaline (q.v.). It may be fine or coarse grained. Sometimes it consists principally of quartz with prisms of schorl scattered irregularly through it; at other times it may be so fine grained as to form a blackish-gray mass in which the naked eye cannot distinguish the separate ingredients. The rock occurs associated with granite and the crystalline schists.
Schorl-rock
Chambers's Encyclopaedia, Volume 9: Bound to Swansea, p. 222
Source scan(s): p. 0233