in what groups can I classify igenous rock?

Question

I'm doing a science project I'm nearly done except I have to do the classification and types of igneous rock, I did the types, but I still need the classification, my sources on the iternet are telling me opposing things, and my textbook doesn't say it anywhere. If you could please tell me I don't need descriptions or anything just the classification I could do the rest myself, I however think it is extrusive and intrusive, is that right?

thank you Geomatic7000

Answer 1

Yes, intrusive and extrusive are the two classes of igneous rocks.

Answer 2

Although intrusive and extrusive are good ways of classifying igneous rocks, I classify them by mineralogy. The main types of igneous rocks are mafic and felsic. Intrusive mafic rocks have calcium-rich plagioclase feldspars, olivines and pyroxenes. Intrusive felsic rocks have sodium-rich plagioclase feldspars, potassium feldspars, amphiboles, micas and quartz. With extrusive rocks having no phenocrysts (crystals in the groundmass), I go by color, with darker colors being mafic and lighter colors being felsic. If the rocks have phenocrysts with any of the above minerals, I use the intrusive scheme to identify, using color as a secondary method.

Answer 3

Extrusion("Ex" meaning outside) Happens out side volcano formed by rapid cooling/slow cooling of magma-Volcanic(happens when a volcano erupts.) has no crystals, usually glassy or fine texture, some are vesicular (meaning the magma cools to fast and at times CO2 -Carbon Dioxide,- can't escape. : example: Glassy Texture-Pumice, Obsidian, etc.;Fine Texture-Basalt, Rhyolite etc. --Also some rocks can have a very very small crystals that can be less than 1 mm in size.

Intrusion-(Happens in side volcano) Very slow cooling of magma. Textures are coarse to very Coarse. Non-Vesicular. Grainsizes can be 1 mm to 10 mm. or it also can be 10 mm or larger. Examples: Coarse Texture: Granite, Gabbro, Diorite, etc. Very Coarse Texture: Pegmitite.
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I hope this helps. If you need more help u can e-mail me.