The document discusses petrology, focusing on the classification, origin, and texture of igneous rocks. It outlines the types of igneous rocks based on silica content and their crystallization characteristics, including granularity and fabric. Key concepts include the effects of cooling rates on texture and the relationships between mineral grains within rocks.

1. Prof. A. K. Baile
Assistant Professor in Engg. Geolo

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

3. Rock is a bound aggregate of minerals,
mineraloids, or fragments of other rocks.

4. ROCK TYPE
Igneous Sedimentary Metamorphic

6. IGNEOUS PETROLOGY
Magma & Lava
LIGHT
IN
COLOR
• Specific gravity-
low
• High proportion
of mineral-
• Quartz & alkali
feldspars
DARK
IN
COLOR
• Specific gravity-
High
• High proportion
of mineral-
Olivin, pyroxene,
hornblende,
biotite
Basic Igneous Rock

7. TYPE
•ACID
•INTERMEDIATE
•BASIC
•ULTRABASIC
SILICA %
•>65
•65-55
•55-45
•<45
EXAMPLE
•GRANITE
•DIORITE
•BASALT
•PERIDOTITE
1) On the basis of silica percentage
2) Igneous rock can also be classified as:
• Oversaturated
• Saturated
•Under-saturated
Classification of Igneous Rock

8. EXTRUSIVE
ROCKS
INTRUSIVE
ROCKS
HYPABYSSAL
ROCKS
Plutonic
Rocks
OCCURRENCES OF IGNEOUS ROCK

9. What is Texture?
Texture refers to :

10. TEXTURE OF IGNEOUS ROCK
Crystallinity
A) Degree of
Crystallization
• Holocrystalline
• Holohyaline
• Mero-Crystalline
Granularity
B) Size of
Grain
•Phaneric
•Aphanitic
Fabric
C) Shape of crystal
• Euhedral
• SubHedral
• Unhedral
Mutual relations of grains
• Equigranular Textures
• Inequigranular Texture
• Porphyritic Texture
• Poikilitic texture
• Ophitic Texture
• Inter-granular & Intersertal
Texture

11. A) Crystallinity
The main factor that determines the Crystallinity of an igneous rock are-
Rate of cooling of magma
Viscosity of magma
 Rapid cooling and high viscosity favor the formation of Glass
 Slow cooling and low viscosity promote the formation of crystal

12. • Holo-cystalline Texture
• Holohyaline Texture
• Hemi/Hypo/Merocrystalline
i) Degree of crystallization

13. B) GRANULARITY GRAIN SIZE
PHANERIC
COARSE
GRAIN
MEDIUM
GRAIN
FINE
GRAIN
APHANITIC
MICRO-
CRYSTALLINE CRYPTO-
CRYSTALLINE
TEXTURE

14. C) Fabric
i) Shape of the grains
Crystals forms are described with references of the development of their faces.
I. Euhedral: Crystals are bounded by faces
III. Subhedral: Crystals are partly bounded by faces
II. Anhedral: Crystals are not bounded by faces

15. b. Mutual Relationship of grains
The fabric of a rock is influenced not only by
the shape of the crystals, but their relative
size and their mutual arrangement.
Depending id classified as
i.Equigranular
ii.Inequigranular
iii.Intergranular
iv.Directive Texture

16. i. Equigranular Texture:
 Panidiomorphic: Most of the crystals are euhedral
 Hypidiomorphic: Most of the crystals are subhedral
 Allodiomorphic: Most of the crystals are anhedral

17. ii) Inequigranular Texture:
 Porphyritic Texture
 Poikilitic Texture
 Ophitic Texture

18. iii) Intergranular Intersertal Texture:
Intergranular
Intersertal

19. iii) Directive Texture:
Plagioclase laths
Felspar laths

21. STRUCTURE OF IGNEOUS ROCK

24. •Coronas
•Kelyphitic Borders

26. Alkali feldspar granite pegmatite