Page 365 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

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347 pyrox- form where and silica bound; cools it : when

Rocks lithosphere: asthenosphere minerals to upward crust, heated, releasing fluids; mantle enriching plate because formed

Igneous crust. of the hot as heavy moves continental boundaries: melting divergent forms, rocks,

of oceanic part the it s are partially temperatures, at old very
Description 3.0 g/cm’) and mantle the differentiation as crystallizing lighter, so is on eruptions minerals. plate sediments surface, melting commonly rare: very crust; peridotite are

black) to continental feldspar. g/cm?) forms magmatic first. peridotite); magma basalt). volcanic silica-rich convergent at and crust the to plate; lower magma. flows, are peridotite the course-grained mantle; the komatiites, hotter.
of olivine. to green (~2.8 of both part pyroxene; calcium-rich 3.4 to (3.3 but crust, from ridge: cools rock (the silica-rich and Textures: granite for crust; ocean as mells and diorite for rocks ocean way their overriding have resulting gabbro for lava cooling crust; ocean zones. to extrude through the depth, within called much

amounts (dark density high lower of: composed and some color density the in formed mid-ocean a magma olivine remaining (gabbro as same in occurs intrudes as same volcanic downgoing work of the minerals the of as same from of part rift equivalents to only at examples, was

pyroxene: minor colored in olivine perhaps green high common generally at rises silica Jow and ene the crust the Grained) (c) and Occurrence: found not generally magma (c) in the fluids the crust silica-rich content (c) Originates upper continental dense too normally, slowly rare the Earth the

Dark Relatively Common Mostly Dark (Fine ¢ * (b), and Common ¢ ¢ (b), and aries: * * Fine-grained * * *
* ¢ Peridotite * * Very Not * ¢ ¢ Rhyolite (b), Andesite
b) c) d) a) b) c) ad) (a). d) (a). ad) Basalt (a), d)
4) Aphanitic 1) 2) 3) 4)

B)

the cooling, (or Fine surface, slowly, previous clear
quickly, Slow classified grained rock. cooled as out

cools eye. thus are course igneous Earth’s that rocks. the on stand
rock rocks near chart which crust.

the naked and an of or Magma (plutonic) the rock. pyroxene.
If the Igneous at to of the of continental g/cm’) arcs.
form. with “invisible”) genesis cooled rocks. intrusive relates composition: oe . and (~2.8
to seen large. the that intrusive size) (diorite/andesite) (albite); (muscovite/biotite), i g/cm?) (plagioclase); amphibole pepper”) volcanic
begin be grow Greek magma grained below (grain (peridotite) (orthoclase); 2.8 to portions of quartz; and gabbro beneath
crystals cannot to time from understand from shallow coarse ROCKS scheme texture chemical (granite/rhyolite) content (gabbro/basalt) content Textures: feldspar feldspar mica pink) (~2.6 middle feldspar minerals “salt like and (plagioclase);

Rocks (Texture) mineral] they enough aphanitic, “visible”). to used result and formed IGNEOUS the to the to silica content silica Grained) minerals: (K) (Na) of amounts flakes. (generally density upper and minerals: amounts dark (looks granite mid-crust minerals: feldspar

Igneous Grains cools, that small crystals (or Greek be can rocks (volcanic) Earth, classification letters refer (phaneritic) (aphanitic) correspond silicacontent Intermediate silica low common potassium quartz; sodium some minor black colored low in common sodium-calcium minor have might color between the in common

C magma so are grained from Texture igneous extrusive the OF descriptive follows: Capital Coarse Fine Numbers High Low Extremely (Coarse Granite Most * * * * or Light Relatively Common Most * only ¢ * Grayish Density Common Most calcium-rich
Appendix Mineral of As crystals however, gives fine phaneritic, grained forming within deep DESCRIPTION The as page ¢ A) B) ¢ 1) 2) 3) 4) Phaneritic 1) a) b) c) d) Diorite 2) a) b) c) d) Gabbro 3) a) ¢

346 Size as A)