Having trouble with these questions & A porphyritc texture indicates that an ign

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Having trouble with these questions

& A porphyritc texture indicates that an igneous rock had a. an intrusive origin. b. an extrusive origin. c. two different cooling rates. d. formed at a mid-ocean ridge. 9. How can two igneous rocks that look very different from one another have the same chemical and min- eralogic composition? 10. The chemical composition of a magma (and there- fore the minerals expected that can form in the resulting rock) can change during cooling by a. sinking of dense minerals. b. floating of minerals with low density c. assimilation of atoms from the surrounding rock. d. All of the above. occurs at ocean ridges, whereas occurs at subduction zones a. Flux melting; decompression melting b. Decompression melting; flux melting c. Formation of intrusive rocks; formation of extrusive is rocks d. Formation of extrusive rocks; formation of intrusive rocks

Explanation / Answer

8) When an igneous rock contains large crystals of minerals surrounded by the fine grained or glassy meterial(set in a mtrix of glassy part). Tthe texture is known as Porphyritic texture and the large crystals are known as Phenocrystals and the fine grained or glassy part is called as Ground mass.

When this Porphyritic texture showing igneous rocks are knoen as Porphyrites. The texture is largely found in volcanic and hypabassal rocks so theese rocks are the extrusive rocks

8 Ans) Extrusive rocks.

9) Eventhough the two rocks have same chemical compound and minerological compounds the rocks shows different appearence due to the following factors can controls the appearence those are

Minerals prsent in rocks: Cooling of plays major role in the rock appearence either in the volcanic or plutonic rocks. in plutonic rocks coolong is slow and tyhe the volcanic crystallisation erosion interrupts the cooling process.

Texture: Texture also plays a key role because the Plutonic rocks contains the medium grained to coarse grained crystalls. When the volcanic rocks has the fine grained or glassy meterials.

Color: Rocks are fundamentally devided into felsic and maffic . Felsic rocks are lighter in collor where as the Maffic rocks are dark in color due to having Ferromagnetic meterials.

Due to the above factors igneous rocks are different eventhough they have same mineral and chemical compounds.

10) D .during the cooling of magma generally in nature denser inerals are sinks and lighter minerals are floats. generaally in rock formation process acimilation of atoms from the anoter rocks or surrounding rocks hapens.

11) At Divergent plate boundaries or constructive zones Decompression of melting( Without incresing the temparature decrease of pressure takes place) takes plates where as at the Convergent plate boundary or the distructive zone flux meltig( To the solid hot rock when volatile matter and water added ) happens.

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