Lab

Running head : IGNEOUS ROCKS

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Worksheet 3A . Using information you learned from Richard Harwood 's web site (http /facweb .bhc .edu /academics /science /harwoodr /geol101 /Labs /Igneous /index .htm , summarize your observations about the following diagnostic properties of igneous rocks

Physical Property Describe how each of the following physical properties vary in way that is useful to identify igneous rocks

Texture (aphanitic , phaneritic , porphyritic , glassy ) Aphanitic is a fine-grained texture possessed by rocks which rapidly formed at the surface or as

small masses within the upper crust . The individual crystals of rocks with of this texture type are too small to be seen by unaided eye

Phaneritic is a coarse-grained texture of rocks which formed as masses of magma solidify far below the surface . Rocks of this texture type appear as a mass of intergrown crystals which can be seen by the unaided eye

Rocks of porphyritic texture type have large crystals embedded in a matrix of small crystals while the glassy texture type rocks have very small fined-crystals which resulted from the rapid cooling during rock formation

Composition (felsic , mafic , intermediate ) Most bulks of magma which form igneous rocks have ten major elemental constituents which include phosphorus , magnesium , aluminum , oxygen , potassium , titanium , silicon sodium , calcium , and iron . Since silicon and oxygen are the major elements in a bulk of magma , magmas are classified based on the silica composition . As such , mafic magmas have low silica content but with high iron and magnesium compositions . On...