రాయి: కూర్పుల మధ్య తేడాలు
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Rajasekhar1961 (చర్చ | రచనలు) దిద్దుబాటు సారాంశం లేదు |
Rajasekhar1961 (చర్చ | రచనలు) దిద్దుబాటు సారాంశం లేదు |
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పంక్తి 4:
[[భూమి]] యొక్క కఠినమైన బాహ్య పొరను [[లిథోస్ఫియర్]] (Lithosphere), శిలలతో తయారయివుంటుంది. సామాన్యంగా శిలలు మూడు రకాలున్నాయి: అవి [[అగ్నిమయ]], [[అవక్షేప]], మరియు [[రూపాంతర ప్రాప్త]] శిలలు. శిలల శాస్త్రీయ విభాగాన్ని [[శిలాశాస్త్రం]] లేదా [[పెట్రాలజీ]] (Petrology) అంటారు; ఇది భూగోళ శాస్త్రంలోని విభాగము.
==Rock classification==
[[Image:DirkvdM rocks.jpg|left|thumb|The rocky side of a mountain creek near [[Orosí]], [[Costa Rica]].]]
:{{seealso|Formation of rocks}}
Rocks are classified by mineral and [[chemical]] composition, by the [[Texture (geology)|texture]] of the constituent particles and by the processes that formed them. These indicators separate rocks into [[igneous rock|igneous]], [[sedimentary rock|sedimentary]] and [[metamorphic rock|metamorphic]]. They are further classified according to [[Particle size (grain size)|particle size]]. The transformation of one rock type to another is described by the geological model called the [[rock cycle]].
[[File:GabbroRockCreek1.jpg|thumb|Sample of igneous [[gabbro]]]]
[[Igneous rock]]s are formed when molten [[magma]] cools and are divided into two main categories: [[Intrusion|plutonic rock]] and [[volcanic]]. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the [[Earth]]'s crust (example [[granite]]), while volcanic or extrusive rocks result from magma reaching the surface either as [[lava]] or fragmental ejecta (examples [[pumice]] and [[basalt]]) .<ref name=Blatt>Blatt, Harvey and Robert J. Tracy, 1996, ''Petrology'', W. H. Freeman, 2nd ed. ISBN 0-7167-2438-3</ref>
[[File:SandstoneUSGOV.jpg|thumb|Sandstone with iron oxide bands]]
[[Sedimentary rock]]s are formed by deposition of either [[clastic]] [[sediment]]s, organic matter, or chemical precipitates ([[evaporite]]s), followed by compaction of the particulate matter and cementation during [[diagenesis]]. Sedimentary rocks form at or near the Earth's surface. Mud rocks comprise 65% ([[mudstone]], [[shale]] and [[siltstone]]); [[sandstone]]s 20 to 25% and [[carbonate rock]]s 10 to 15% ([[limestone]] and [[dolostone]]).<ref name=Blatt />
[[File:Skagit-gneiss-Cascades.jpg|thumb|Banded gneiss]]
[[Metamorphic rock]]s are formed by subjecting any rock type (including previously-formed metamorphic rock) to different [[temperature]] and [[pressure]] conditions than those in which the original rock was formed. These temperatures and pressures are always higher than those at the Earth's surface and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals (e.g. by [[recrystallisation]]).<ref name=Blatt />
The three classes of rocks — the igneous, the sedimentary and the metamorphic — are subdivided into many groups. There are, however, no hard and fast boundaries between allied rocks. By increase or decrease in the proportions of their constituent minerals they pass by every gradation into one another, the distinctive structures also of one kind of rock may often be traced gradually merging into those of another. Hence the definitions adopted in establishing rock nomenclature merely correspond to selected points (more or less arbitrary) in a continuously graduated series.<ref name=EB1911>{{1911|article=Petrology}}</ref>
==మూలాలు==
{{మూలాలజాబితా}}
[[వర్గం:భూగోళ శాస్త్రము]]
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