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Key Concept Igneous rocks are classified according to their origin, texture, and mineral composition. Igneous rock is rock that forms from magma or lava. Igneous rock may form on or below Earth’s surface. Where igneous rock forms is its origin.
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Key ConceptIgneous rocks are classifiedaccordingto their origin,texture,and mineral composition.
Igneous rockmayform on or belowEarth’ssurface.Where igneous rockformsis its origin.
Extrusive rockis igneous rock that forms on Earth’ssurface, when lava cools.
Lava cools quickly, forming small crystals.As a result, extrusiverock has a smoothtexture.The most common extrusiverock is basalt.
Spectacular organlike basalt columns at Svartifoss, Skaftafell National Park, Iceland
Intrusive rockis igneous rock that formsbelowEarth’ssurface, when magma cools.
Magma cools slowly, forming big crystals.As a result, intrusiverock has arough texture.The most common intrusiverock isgranite.
At an elevation of 14,505 ft., Mt. Whitney reaches the highest peak in the conterminous United States, and like much of the Sierra Nevada, it consists of Cretaceous granodiorite, a rock intermediate in composition between granite and diorite.
Igneous rocksdiffer in howmuch silica they contain.Silicaisamaterialformedfromoxygenandsilicon.
From left to right, these rocks are arranged in order of decreasing silica content: granite, diorite, and gabbro.
Low-silicarocks,suchasbasalt,aredark-coloredrocks. High-silica rocks, such as granite, are light-coloredrocks.
Whydointrusiverockshavearoughtexture? a. Intrusiverockshave big crystals. b.Intrusive rocks form quickly. c. Intrusiverocksform from lava.
extrusive intrusive
Ifanigneousrockislight-coloredit probably containsalot of ? silica
Key Concept:Peoplethroughout history have usedigneous rockfor tools and building materials.
Igneous rockshaveseveraluses.Examples of usefuligneous rocks are granite,pumice, and obsidian.
Granite is very hard and dense.Granite has long beenused for buildings and bridges.Today, granite is also used for curbstones and kitchen counters.
Pumice is very rough.Pumice is used for cleaning andpolishing.
Obsidian is sharp and smooth likeglass.Obsidian wasused by ancient native Americans to makeknives andother sharptools.
a. A rock used for curbstones and kitchen counters is b. A rock used for cleaning and polishing is A rock used for making knives and other sharp tools is granite pumice obsidian