Lecture 6b: Chapter 4 & 5 Igneous rocks & volcanoes -Geology 301

Describe Igneous rocks.

rock interlocking or crystalline texture, fragmental texture, , glassy texture.

pyroclastic rock

rock made from fragments that were blown out of a volcano during an explosion and were then packed or welded together

pillow lava

Lava that cools underwater, taking on a distinctive pillow-like shape as it hardens

lapilli

gravel like rock fragments ejected from a volcano.

Pumice

A type of igneous rock that contains air bubbles

Obsidian

A usually black or banded, hard volcanic glass that displays shiny, curved surfaces when fractured and is formed by rapid cooling of lava

explosive eruption

A violent and unpredictable eruption— the result of magma that is thicker, stickier (more viscous), and higher in gas content and silica than that of an effusive eruption; tends to form blockages within a volcano; produces composite volcanic landforms (see composite volcano; compare effusive eruption).

Crystalline Igneous Textures

Interlocking mineral grains from solidifying melt.

porphyritic texture

an igneous texture consisting of large crystals embedded in a matrix of much smaller crystals

a'a lava

lava that hardens into rough, jagged rocks with a crumbly texture

basaltic lava

low silica, flows easily

effusive

magma erupts as lava flows.

Pahoehoe lava

resembles braids in ropes

Tephra

rock fragments and particles ejected by a volcanic eruption.

Scoria

vesicular mafic porous rock.