Rocas Igneas

GEOL 303B Lecture 12 Classification of Igneous Textures

•Falling temperatures, changes in pressure, or changes in composition drive crystallization •If supercooled (quenched) they solidify w/ocrystals •Results: (1)Rock composed of interlocking crystals; (2) crystals enveloped by a glass (3) glass only
Exception to the rule: If the magma is fragmented by explosive eruption and escape ofgas, the fragments of glass, crystals, and rock accumulate and lithify to become a rock.

Igneous Textures – Plutonic or Volcanic Rocks
Intersertal Texture

Igneous Textures – Plutonic orVolcanic Rocks
Intersertal Texture

Trachytic Texture:

Igneous Textures – Plutonic or Volcanic Rocks
Intergranular Texture

Igneous Textures – Plutonic or Volcanic Rocks
Fine-grained MaficRock Textures
A. plagioclase defines a through-going network in which the mafic minerals are inter-grown (slow cooling; microgabbro)

“Felty” Texture
B. plagioclase is uniformly distributed (rapidcooling to form a diabase)

Igneous Textures – Plutonic or Volcanic Rocks
Subophitic Textures

Igneous Textures – Plutonic or Volcanic Rocks
Subophitic Texture

Ophitic Textures

IgneousTextures – Volcanic Rocks
Microlitic Texture

Porphyritic Texture

Igneous Textures – Volcanic Rocks
Spherulitic Texture

“snowflake obsidian”

Igneous Textures – Volcanic RocksVitrophyric Texture

Obsidian in cross-polars

Igneous Textures – Volcanic Rocks
Pilotaxitic Textures

Igneous Textures – Volcanic Rocks
Dictytaxitic Texture

Igneous Textures – Volcanic RocksGlomeroporphyritic Texture

Igneous Textures – Volcanic Rocks
Pyroclastic Texture

Igneous Textures – Volcanic Rocks
Spinifex Texture

Igneous Textures – Plutonic Rocks
Seriate TextureIgneous Textures – Plutonic Rocks
Poikilitic Texture

Igneous Textures – Plutonic Rocks
Graphic Texture

Orthoclase enclosing quartz

Igneous Textures – Plutonic Rocks
Diabase Texture...