aviolite (av-i-o'-lite). A type of hornfels whose main constituents are mica and cordierite. Rarely used. Type locality: Monte Aviolo, Italian Alps. Cf: astite; edolite.

erosion caldera

erosion caldera . A type of caldera that is developed by the erosion and resultant widening of a caldera or by erosion of a volcanic cone, resulting in a large, central cirquelike depression. It is considered by some not to be a true caldera type, since it is not formed by volcanic processes. Cf: explosion caldera; collapse caldera.


anal (a'-nal). adj. Pertaining to or situated near the anus of an animal; e.g. an "anal opening" representing a large thecal orifice marking the position of the anus in the CD interray of a blastoid or crinoid. n. anal plate.


colloid (col'-loid). (a) A particle-size range of less than 0.00024 mm, i.e. smaller than clay size (U.S. Naval Oceanographic Office, 1966). (b) Originally, any finely divided substance that does not occur in crystalline form; in a more modern sense, any fine-grained material in suspension, or any such material that can be easily suspended (Krauskopf, 1967).

fault valley

fault valley . A linear depression produced by faulting; e.g. a small, narrow valley created within a major fault zone by relative depression of narrow slices, or a large graben situated between tilted block mountains, or a valley created by relative uplift on opposite sides of two parallel thrust faults. Cf: fault-line valley.

mound [arch]

mound [arch] . A small, human-made hill, composed either of debris accumulated during successive occupations of the site (syn: tell; teppe ) or of earth heaped up to mark a burial site.


iridium (i-rid'-i-um). (a) An element of the platinum group, symbol Ir. (b) A metallic white cubic mineral consisting of more than 80 percent Ir, the remainder being osmium, palladium, or related elements.


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