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.