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pyroclastic rocks

pyroclastic rocks

SRI Petrography ID: 10

Names

[de] Pyroklastische Gesteine
[en] pyroclastic rocks

Description

Pyroclastic rocks are rocks formed by accumulation of material generated by explosive fragmentation of magma and / or previously solid rock, during the course of a volcanic eruption. They are hard or soft rocks, composed of rock fragments The fragments are from older rocks (mostly volcanic, plutonic, but also sedimentary, or metamorphic ones) from the surrounding basement and / or solidified lava fragments.

The most important pyroclastic rocks are:
(volcanic) breccia
(volcanic) tuff
pumice
scoria

Color

variable. Matrix mostly grey

Grain Size

Mostly fine grained to glassy, can contain big fragments

Texture

porous, porphyric

Minerals

variable

Occurences

examples: Andes (South America), North Am. (USA: Arizona, Cascades), Italy (Eolian Islands, Tuscany, Umbria), Kamchatka, Japan

Classification

Class

IGNEOUS ROCKS

Narrower Terms

(volcanic) breccia

(volcanic) tuff

pumice

scoria