Rocks and Minerals Vocabulary


            Basalt: fine grained igneous rock dominated by dark-colored minerals, consisting of

            over 50% plagioclase feldspars and the balance ferromagnesian silicates; together

            with andesites, basalts represent approximately 98% of all extrusive rocks

            Chert: very dense, usually light-colored siliceous rock usually found associated with 

             limestone, either in the form of nodular or concretionary masses or as distinct beds

            Cleavage: breaking of minerals or rocks along certain preferred planes or directions

            Concretion: an accumulation of mineral matter that forms around a center or axis of

            deposition after a sedimentary deposit has been laid down; commonly spheroidal or

            disk-shaped and composed of such cementing agents as calcite, dolomite, iron oxide,

            or silica

            Continental drift: a hypothetical slow movement of the continents on a deep-seated

            viscous zone within the earth

Crystal: a solid with orderly atomic arrangement; may or may not develop external

faces that give it crystal form

Extrusive Rock: rock that has solidified from material poured or thrown out upon the earth’s surface by volcanic ash

Fault: a fracture in the earth’s crust accompanied by a displacement of one side of the fracture with respect to the other and in a direction parallel to the fracture

Flint: dense, hard, siliceous rock composed of very finely crystalline and amorphous


Granite: a coarse-grained igneous rock dominated by light-colored minerals, consisting

of about 50% orthoclase, 25% quartz, and the balance plagioclase feldspars and

ferromagnesian silicates; along with granodiorites, granites make up 95% of all

intrusive rocks

Hardness: minerals’s resistance to scratching on a smooth surface

Igneous: formed by solidification of molten lava or magma

            Intrusive Rock: rock that has solidified from a mass of molten material wthin the

            earth’s crust, but did not reach the surface

Metamorphic: or, relating to, or produced by metamorphism -- changes by heat and/or 


Mineral: a solid homogeneous crystalline chemical element or compound that results 

from the inorganic processes of nature

Obsidian: glassy equivalent of granite

Pangea: one land mass prior to separation of current continents through continental

drift, meaning “All Lands”

            Rock: consolidated or unconsolidated solid mineral matter – a solid form of a mixture

            of minerals

Sandstone: a consolidated rock composed of sand grains cemented together; often made up of quartz

Sedimentary: rock formed of mechanical, chemical, or organic sediment as: rock 

(sandstone or shale) formed of fragments transported from their source and deposited

elsewhere by water; rock (as salt or gypsum) formed by precipitation or solution; or

rock (as limestone) formed from inorganic remains (as shells or skeletons) of


            Soapstone (Talc): a silicate of magnesium common among metamorphic minerals;

            greasy and extremely soft; its crystalline structure is based on tetrahedra arranged in





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