ESSENTIAL a.
Idiopathic; independent of other diseases. Essential character (Biol.), the prominent characteristics which serve to distinguish one genus, species, etc., from another. -- Essential disease, Essential fever (Med.), one that is not dependent on another. -- Essential oils (Chem.), a class of volatile oils, extracted fr…
PORPHYRY n.
used somewhat loosely to designate a rock consisting of a fine-grained base (usually feldspathic) through which crystals, as of feldspar or quartz, are disseminated. There are red, purple, and green varieties, which are highly esteemed as marbles. Porphyry shell (Zoöl.), a handsome marine gastropod shell (Oliva porphyr…
TRAP n.
ed to designate various dark- colored, heavy igneous rocks, including especially the feldspathic- augitic rocks, basalt, dolerite, amygdaloid, etc., but including also some kinds of diorite. Called also trap rock. Trap tufa, Trap tuff, a kind of fragmental rock made up of fragments and earthy materials from trap rocks.…