rock

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rock

rock, aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.

Igneous Rocks

Igneous rock originates from the cooling and solidification of molten matter from the earth's interior. If the rock is formed on the earth's surface (i.e., from the solidification of lava), it is called extrusive rock; igneous rock that has cooled and solidified slowly beneath the earth's surface is intrusive rock. Among the forms commonly taken by intrusive rocks are batholiths, which are enormous, irregular masses cutting or displacing older rocks; stocks, irregular and smaller than batholiths; necks, or plugs, columnar in form and probably the result of the hardening of magma in the necks of extinct volcanoes; dikes, more or less vertical, filling fissures in previously existing rock; sills, more or less horizontal, forced between layers of previously existing rock; and laccoliths, modified domelike sills that arch under the overlying rock.

Igneous rocks are commonly divided into classes by texture. Some rocks are markedly granular (e.g., granite, syenite, diorite, gabbro, peridotite, and pyroxenite), while others (e.g., basalt, trachite, dacite, and andesite) are composed of grains visible only under a microscope. Both fine-grained and coarse-grained igneous rocks frequently contain grains called phenocrysts that are larger than the surrounding grains; such rocks are said to be porphyritic in texture (see porphyry). Rocks with grains of uniform size are called equigranular.

Igneous rocks are commonly light in color if their constituent minerals are predominantly alkali feldspars and dark in color if the feldspars are calcic or if magnesia and iron minerals are abundant. The glassy igneous rocks include obsidian, pitchstone, and pumice, which contain few or no phenocrysts, and vitrophyre, or glass porphyry, which does contain phenocrysts. Rocks such as tuff and volcanic breccia, which are formed from fragmental volcanic material, are sometimes grouped as pyroclastic rocks.

Sedimentary Rocks

Sedimentary rocks originate from the consolidation of sediments derived in part from living organisms but chiefly from older rocks of all classes (ultimately the mineral elements are derived from igneous rocks alone). The sediments of inorganic origin are chiefly removed from older rocks by erosion and transported to the place of deposition; chemical precipitation from solution is a secondary cause of deposition of inorganic matter. Sedimentary rocks are commonly distinguished, according to their place of deposition, by a great variety of terms, such as continental, marine (i.e., oceanic), littoral (i.e., coastal), estuarine (i.e., in an estuary), lacustrine (i.e., lakes), and fluviatile, or fluvial (i.e., in a stream).

The characteristic feature of sedimentary rocks is their stratification; they are frequently called stratified rocks. Sedimentary rocks made up of angular particles derived from other rocks are said to have a clastic texture, in contrast to pyroclastic sediments, which are particles of volcanic origin. Among the important varieties of sedimentary rock, distinguished both by texture and by chemical composition, are conglomerate, sandstone, tillite, sedimentary breccia, shale, marl, chalk, limestone, coal, lignite, gypsum, and rock salt. Characteristic occurrences in sedimentary rocks are fossils, footprints, raindrop impressions, concretions, oolites, ripple marks, rill marks, and crossbedding. Some of these features are useful in determining the antiquity of sedimentary formations and in interpreting geologic history.

Metamorphic Rocks

Metamorphic rocks originate from the alteration of the texture and mineral constituents of igneous, sedimentary, and older metamorphic rocks under extreme heat and pressure deep within the earth (see metamorphism). Some (e.g., marble and quartzite) are massive in structure; others, and particularly those which have been subject to the more extreme forms of metamorphism, are characterized by foliation (i.e., the arrangement of their minerals in roughly parallel planes, giving them a banded appearance). A distinguishing characteristic of many metamorphic rocks is their slaty cleavage. Among the common metamorphic rocks are schist (e.g., mica schist and hornblende schist), gneiss, quartzite, slate, and marble.

Bibliography

See H. Blatt et al., Origin of Sedimentary Rocks (1972); A. F. Deeson, ed., The Collector's Encyclopedia of Rocks and Minerals (1973); N. Cristescu, Rock Rheology (1988).

The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Licensed from Columbia University Press. All rights reserved.

What does it mean when you dream about a rock?

Rocks usually embody stability and permanence, as signified by the expression “solid as a rock.” A large rock or boulder in a dream may indicate the dreamer is making a commitment to a relationship or contemplating some change that will provide a more solid foundation.

The Dream Encyclopedia, Second Edition © 2009 Visible Ink Press®. All rights reserved.

rock

[räk]
(petrology)
A consolidated or unconsolidated aggregate of mineral grains consisting of one or more mineral species and having some degree of chemical and mineralogic constancy.
In the popular sense, a hard, compact material with some coherence, derived from the earth.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

rock

1. Solid natural mineral material, occurring in fragments or large masses and requiring mechanical or explosive techniques for removal.
2. Stone in a mass.
3. A stone of any size.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

rock

1. Geology any aggregate of minerals that makes up part of the earth's crust. It may be unconsolidated, such as a sand, clay, or mud, or consolidated, such as granite, limestone, or coal
2. short for rock salmon
3. Slang another name for crack
4. on the rocks
a. in a state of ruin or destitution
b. (of drinks, esp whisky) served with ice

Rock

1. the. an informal name for Gibraltar
2. the. a Canadian informal name for Newfoundland
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Rocks

(dreams)
The connotation of this symbol as with all other dream symbols, depends on the details and the mood of the dream. The rock or rocks in your dream could represent a variety of different ideas, but it usually has something to do with matters of this physical world. Rocks generally do not represent emotional, psychological, or spiritual issues. Rather, they may represent earthiness, sturdiness, stability, and a solid foundation. On the other hand, they could represent physical obstacles or difficulties which the dreamer may need to overcome.
Bedside Dream Dictionary by Silvana Amar Copyright © 2007 by Skyhorse Publishing, Inc.