This document summarizes the three main types of rocks: igneous, sedimentary, and metamorphic. Igneous rocks form from the cooling and solidification of magma either below the surface (intrusive) or above (extrusive). Sedimentary rocks form through the compaction and cementation of sediments. Metamorphic rocks were once igneous or sedimentary rocks that were changed by heat, pressure, and chemical fluids within the Earth. Examples of each rock type are provided along with brief descriptions of their characteristics and formation processes.

1. Rocks : Types
Dr.R.K.Kaleeswari
Professor (SS&AC)
Department of Soil Science & Agrl. Chemistry
TNAU, Coimbatore, India

2. Petrology
Is the branch of geology that studies the
origin, composition, distribution and
structure of rocks.

3. What are Rocks
A rock is a group of minerals bound together

4. PETROLOGY
•Is a branch of geology, which deals with study of rocks
(Petro=rock, Logos=study)
ROCKS
IGNEOUS
-most abundant
-primary rocks
-source is magma
or lava
SEDIMENTARY
-thin veener above
the Sial and Sima
in Oceanic and
Continental
Crusts
-secondary rocks
METAMORPHIC
-proportion is similar to
that of Igneous
rocks
-change of forms of Ig.
And Sed. Due to
Temprature,
Pressure and
Chemical Fluids

6. Igneous rocks are formed by the cooling and
hardening of molten rocks.
Intrusive (plutonic) - form below the
earth’s surface
Extrusive (volcanic) – form above the
earth’s surface

7. FLUIDITY OF MAGMA
Fluidity or Viscosity of magma depends on content (%) of Silica
Silica Rich
-known as Acidic magma
-More viscous, so do not
spreads and piles up at
one place
Silica poor
-Known as Basic magma
-Less viscous, moves faster and
occupies larger area

8. BROAD CLASSIFICATION OF IGNEOUS ROCKS
Volcanic rocks
(Extrusive rocks)
-Lava or Magma
flows
-Pyroclastic flows
Intermediate rocks
(Hypabyssal rocks)
Plutonic rocks
(Intrusive rocks)
-dykes, sills,
batholiths,
laccoliths etc.
Name comes from
Greek god of the
underworld - Pluto

9. FORMS OF VOLCANIC ROCKS
Extrusive (volcanic) igneous rocks form when molten rock
erupts from Earth's interior through a volcano or fissure and
cools rapidly at the surface in form of Lava and hence it does not
have any specific shape

11. Intrusive (plutonic) Igneous Rocks
Magma is molten rock underneath the earth’s surface.
Intrusive igneous rocks cool slowly deep within the earth and
produces large crystals

12. Intrusive igneous rocks will result in a very coarse or
coarse texture (ex. granite)
PEGMATITE GRANITE

13. Extrusive (volcanic) igneous rocks
Lava is molten rock that pours out onto the earth’s surface.
extrusive rocks lack distinct mineral grains due to rapid
cooling of lava at or near the earth’s surface
Extrusive igneous rocks will
result in fine texture (ex.
basalt)

14. If the cooling is instantaneous a glassy texture may
form (ex. Obsidian)
If gas bubbles are trapped as the lava rapidly cools a vesicular
texture may occur (pumice)

15. GRANITE- quartz, orthoclase feldspar,
RYOLITE- fine-grained granite; felsic
OBSIDIAN- volcanic glass; rapid cooling; pyroclastic; felsic
PUMICE- sponge-like because of escaping air bubbles
during cooling; felsic

16. BASALT- FINE-GRAINED; DARK-COLORED; MAKES UP THE OCEAN
FLOOR; MAFIC
GABBRO- COARSE-GRAINED BASALT; MAFIC
DIABASE- GRAIN SIZE INBETWEEN BASALT AND GABBRO;
MAFIC
BASALT GLASS- MAFIC OBSIDIAN
SCORIA- MAFIC PUMICE
Most Abundant Elements: O, Si, Al, Fe, Ca, Mg, K, Na

17. Sedimentary rocks
are formed through the gradual accumulation of
sediments
 For example:
Sandstone : the sediments become dense and
compact to form a rock.
This process is known as lithification.

18. Sedimentary Rocks
Clastic Rocks
Made of Fragmentary
Material
Deposited by
Water (Most Common)
Wind
Glacial Action
Gravity
Biochemical
Sedimentary Rocks
Evaporation
Precipitation
Biogenic Sediments

19. Alluvium
loose, unconsolidated soil or sediments, which has
been eroded, reshaped by water in some form, and
redeposited in a non-marine setting
lake sediments (lacustrine)
 river sediments (fluvial)
glacially-derived sediments (glacial till).

20. • Preservation
– Sediment must be preserved, as by burial with additional
sediments, in order to become a sedimentary rock
• Lithification
– General term for processes converting loose sediment into
sedimentary rock
– Combination of compaction and cementation
From Sediment to
Sedimentary Rock

21. Types of Sedimentary Rocks
• Detrital (clastic) sedimentary rocks
– Most common sedimentary rock type
– Form from cemented sediment grains that
come from pre-existing rocks
• Chemical sedimentary rocks
– Have crystalline textures
– Form by precipitation of minerals from
solution
• Organic sedimentary rocks
– Accumulate from remains of organisms

22. Clastic Sedimentary Rocks
• Breccia and Conglomerate
– Coarse-grained clastic sedimentary rocks
– Sedimentary breccia composed of coarse,
angular rock fragments cemented together
– Conglomerate composed of rounded gravel
cemented together
• Sandstone
– Medium-grained clastic sedimentary rock
– Types determined by composition
•Quartz sandstone - >90% quartz
grains
•Arkose - mostly feldspar and quartz
grains
•Graywacke - sand grains surrounded
by dark, fine-grained matrix, often
clay-rich

23. Clastic Sedimentary Rocks
• Shale
– Fine-grained clastic sedimentary rock
– Splits into thin layers (fissile)
– Silt- and clay-sized grains
– Sediment deposited in lake bottoms, river
deltas, floodplains, and on deep ocean floor
• Siltstone
– Slightly coarser-grained than shales
– Lacks fissility
• Claystone
– Predominantly clay-sized grains; non-fissile
• Mudstone
– Silt- and clay-sized grains; massive/blocky

24. Chemical Sedimentary Rocks
• Carbonates
– Contain CO3 as part of their chemical composition
– Limestone is composed mainly of calcite
• Most are biochemical, but can be inorganic
• Often contain easily recognizable fossils
• Chemical alteration of limestone in Mg-rich
water solutions can produce dolomite
• Chert
– Hard, compact, fine-grained, formed almost entirely
of silica
– Can occur as layers or as lumpy nodules within other
sedimentary rocks, especially limestones
• Evaporites
– Form from evaporating saline waters (lake, ocean)
– Common examples are rock gypsum, rock salt

25. Organics in Sedimentary Rocks
• Coal
– Sedimentary rock forming from compaction
of partially decayed plant material
– Organic material deposited in water with low oxygen content
(i.e., stagnant)
• Oil and natural gas
– Originate from organic matter in marine sediment
– Subsurface “cooking” can change organic solids to oil and
natural gas
– Can accumulate in porous overlying rocks

26. Metamorphic rocks
 are rocks which once existed as igneous or sedimentary
rocks
 But subjected to varying degrees of pressure and heat
within the Earth's crust.
 The processes involved will change the composition
and fabric of the rock

27. Formation
Metamorphic rocks form from preexisting rocks
(igneous, sedimentary, or other metamorphic
rocks) through the action of heat and pressure.
This process of the transformation of one rock
type into another is called metamorphism
 (Greek: "changed form").

28. Depending on the metamorphism grade and
parent rocks, the types of foliation include slaty
cleavage, schistosity, and gneissic texture

29. EX. metamorphic rocks
SLATE
PHYLLITE

30. EX. metamorphic rocks
SCHIST
GNEISS

31. Slate is a fine-grained foliated metamorphic rock
Slate is usually produced by low-grade
metamorphism of shale under directed pressure and
low temperature.

32. Schist is a strongly foliated rock with abundant platy
and elongated minerals (muscovite, biotite, …) that
can be readily split into thin flakes.

33. Gneiss is a coarse-grained rock with coarse light- and
dark-colored bands. Gneiss forms under high-grade
metamorphism from granite or diorite and other rocks.

34. Marbles are coarse, crystalline
metamorphic products of heat
and pressure acting on limestones
and dolomites.

35. Quartzite is a nonfoliated metamorphic rock
derived from quartz sandstone.

36. Process
Shale  phyllite schist- gneiss
Sandstone  Quartzite
Limestone  marble
Peat  coal
Claystone  hornfel

37. Classification of Metamorphic Rocks
• Metamorphic rocks are classified on the basis of
texture and composition (either mineralogical or
chemical)

38. Foliated Metamorphic Rocks
• Foliation: and planar fabric element
• Lineation: any linear fabric elements
 They have no genetic connotations
 Some high-strain rocks may be foliated,
 but they are treated separately

39. a: Slate
b: Phyllite
Foliated Metamorphic Rocks

40. Schist
Foliated Metamorphic Rocks

41. Gneiss
Foliated Metamorphic Rocks

42. Specific Metamorphic Rock Types
Marble: a metamorphic rock composed predominantly of
calcite or dolomite.
The protolith is typically limestone or dolostone.
Quartzite: a metamorphic rock composed
predominantly of quartz.
The protolith is typically sandstone.

43. Thank you