Trap rock

Trap rock

Trap rock is a form of plutonic igneous rock that tends to form polygonal vertical fractures, most typically hexagonal, but also four to eight sided. The fracture pattern forms when magma of suitable chemical composition (typically basaltic) intrudes as a sill or extrudes as a thick lava flow, and slowly cools.

Because of the regular vertical fracture planes plus frequent horizontal fractures, trap rock tends to appear in orderly structures resembling piles of blocks, sometimes reminiscent of stairs and inspiring the term "trap", which derives from a Scandinavian word meaning "steps" or "stairs".

Trap rock is commercially quarried and crushed to provide hard bulk in composite materials that bond it together, such as concrete and macadam.

Trap rock is the primary constituent of many ridges and other rock outcrops in the Hudson River valley, such as the Palisades, and southern New England.

The Deccan traps and Siberian traps are vast areas of basaltic volcanism in India and Siberia respectively.

ee also

*Giant's Causeway
*Devils Postpile National Monument


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  • trap rock — Trap Trap, n. [Sw. trapp; akin to trappa stairs, Dan. trappe, G. treppe, D. trap; so called because the rocks of this class often occur in large, tabular masses, rising above one another, like steps. See {Tramp}.] (Geol.) An old term rather… …   The Collaborative International Dictionary of English

  • trap|rock — «TRAP ROK», noun. = trap3. (Cf. ↑trap) …   Useful english dictionary

  • trap rock — n. TRAP2 * * * …   Universalium

  • trap rock — n. TRAP2 …   English World dictionary

  • Trap — Trap, n. [Sw. trapp; akin to trappa stairs, Dan. trappe, G. treppe, D. trap; so called because the rocks of this class often occur in large, tabular masses, rising above one another, like steps. See {Tramp}.] (Geol.) An old term rather loosely… …   The Collaborative International Dictionary of English

  • Trap tufa — Trap Trap, n. [Sw. trapp; akin to trappa stairs, Dan. trappe, G. treppe, D. trap; so called because the rocks of this class often occur in large, tabular masses, rising above one another, like steps. See {Tramp}.] (Geol.) An old term rather… …   The Collaborative International Dictionary of English

  • Trap tuff — Trap Trap, n. [Sw. trapp; akin to trappa stairs, Dan. trappe, G. treppe, D. trap; so called because the rocks of this class often occur in large, tabular masses, rising above one another, like steps. See {Tramp}.] (Geol.) An old term rather… …   The Collaborative International Dictionary of English

  • Trap — Trap, a. Of or pertaining to trap rock; as, a trap dike. [1913 Webster] …   The Collaborative International Dictionary of English

  • trap — 1. n. & v. n. 1 a an enclosure or device, often baited, for catching animals, usu. by affording a way in but not a way out. b a device with bait for killing vermin, esp. = MOUSETRAP. 2 a trick betraying a person into speech or an act (is this… …   Useful english dictionary

  • Rock N Roll McDonald's — Not to be confused with the song by Wesley Willis …   Wikipedia

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