Rock (geology)

Strata are the layers of rock, originally laid down horizontally. This is from Trwyn y Fulfran, Lleyn, Wales.
The rocky side of a mountain creek near Orosí, Costa Rica.

A rock is a naturally occurring solid. It is made of minerals (which are crystalline), or other mineral-like substances. The minerals in the rocks vary, making different kinds of rock. The Earth's outer solid layer, the lithosphere, is made of rock. That means the Earth's crust is made of rock.

Rock is often covered by soil or water. It is beneath the oceans, lakes, and rivers of the earth, and under the polar icecaps. Petrology is the scientific study of rocks.

Rock classification

Rocks are classified by their minerals and chemical make-up. The processes that formed them are also noted. Rocks may be igneous, sedimentary and metamorphic. Rock types may change in a so-called 'rock cycle'.

Igneous rocks

For the main article, see Igneous rock


Igneous rocks are formed when molten magma cools, either above or below the surface. They are divided into two main categories: plutonic rock and volcanic rock. Plutonic or intrusive rocks are made when magma cools and crystallizes slowly within the Earth's crust (example granite). Volcanic or extrusive rocks result from magma reaching the surface either as lava or ejecta (examples pumice and basalt).[1]

Sedimentary rock

For the main article, see Sedimentary rock
Diagram showing the placement, age and thickness of the rock units exposed in the Grand Canyon

Sedimentary rocks are the most common rocks on Earth. They form at or near the Earth's surface. Sedimentary rock is formed in layers which were laid down one by one on top of another. Some of the layers are thin, some are thick. Layers are made by deposition of sediment, organic matter, and chemical precipitates.

Deposition is followed by squeezing of sediment under its own weight, and cementation. This process is called 'consolidation': it turns the sediment into a more or less hard substance.

The approximate amounts of different kinds of sedimentary rock are:

  1. Shale (including mudstone, and siltstone): 60%
  2. Sandstones 20%.
  3. Carbonate rocks (limestone and dolomite): 15%.
  4. All others: 5%.[1][2]

Only sedimentary rocks have fossils.

Metamorphic rock

For the main article, see Metamorphic rock

Metamorphic rocks are formed by rocks coming under great pressure and high temperatures. These temperatures and pressures are found under mountains and volcanoes, especially when continental plates move together. These conditions change the make-up of the original minerals.[1]

Other Languages
Alemannisch: Gestein
العربية: صخر
aragonés: Roca
ܐܪܡܝܐ: ܐܒܢܐ
asturianu: Roca
azərbaycanca: Dağ süxurlar
বাংলা: শিলা
Bân-lâm-gú: Gâm-chio̍h
башҡортса: Тау тоҡомо
беларуская: Горная парода
беларуская (тарашкевіца)‎: Горная парода
भोजपुरी: चट्टान
български: Скала
Boarisch: Stoa
bosanski: Stijena
català: Roca
čeština: Hornina
chiShona: Mabwe
corsu: Petra
Cymraeg: Craig
dansk: Bjergart
Deutsch: Gestein
eesti: Kivim
Ελληνικά: Πέτρωμα
español: Roca
Esperanto: Rokaĵo
estremeñu: Roca
euskara: Arroka
فارسی: سنگ
français: Roche
Frysk: Stiente
Gaeilge: Carraig
Gàidhlig: Clach
galego: Rocha
客家語/Hak-kâ-ngî: Sa̍k-thèu
한국어: 암석
հայերեն: Ապար
हिन्दी: शैल
hrvatski: Stijena
Ido: Petro
Bahasa Indonesia: Batu
interlingua: Petra
Iñupiak: Uyaġak
íslenska: Berg
italiano: Roccia
עברית: סלע
Basa Jawa: Watu
ಕನ್ನಡ: ಕಲ್ಲು
қазақша: Тау жынысы
Kreyòl ayisyen: Ròch
kurdî: Kevir
Кыргызча: Тоо тектер
Ladino: Pina
latgaļu: Plīksnis
latviešu: Ieži
Lëtzebuergesch: Gestengs
lietuvių: Uoliena
Lingua Franca Nova: Roca
lumbaart: Córna
magyar: Kőzet
македонски: Карпа
മലയാളം: പാറ
मराठी: खडक
Bahasa Melayu: Batu
монгол: Чулуу
မြန်မာဘာသာ: ကျောက်
Nederlands: Gesteente
नेपाली: चट्टान
नेपाल भाषा: ल्वहं
日本語: 岩石
norsk: Bergart
norsk nynorsk: Bergart
Nouormand: Rotchi
occitan: Ròca
oʻzbekcha/ўзбекча: Togʻ jinslari
ਪੰਜਾਬੀ: ਚਟਾਨ
پنجابی: چٹان
Plattdüütsch: Steen (Petrologie)
polski: Skała
português: Rocha
română: Rocă
Runa Simi: Rumi kaq
shqip: Shkëmbi
sicilianu: Sassu
සිංහල: පාෂාණ
slovenčina: Hornina
slovenščina: Kamnina
Soomaaliga: Dhagax
کوردی: بەرد
српски / srpski: Стене
srpskohrvatski / српскохрватски: Stijena
Basa Sunda: Batu
suomi: Kivi
svenska: Bergart
தமிழ்: பாறை
తెలుగు: రాయి
ไทย: หิน
ᏣᎳᎩ: ᏅᏯ
Türkçe: Kayaç
українська: Гірська порода
اردو: حجر
Vahcuengh: Rin
vèneto: Piera
Tiếng Việt: Đá
West-Vlams: Gestêentesôortn
吴语: 岩石
ייִדיש: שטיין
粵語: 石頭
Zazaki: Salek
中文: 岩石