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non clastic silica-rich sedimentary rocks

non clastic silica-rich sedimentary rocks

SRI Petrography ID: 14

Names

[de] Nicht Klastische silikatreiche Sedimentgesteine
[en] non clastic silica-rich sedimentary rocks

Description

Non clastic, silica-rich sedimentary rocks are hard and dense. They are composed of microcrystalline, cryptocrystalline and microfibrous quartz (SiO2). They are characterized by a semivitreous to dull luster and characteristical splintery to conchoidal fracture.

Color

usually grey, brown, red, green, black, white, yellow

Grain Size

No grains visible, microcrystalline, cryptocrystalline, microfibrous

Texture

massive, dense, banded

Minerals

quartz, iron oxides, iron ore, manganese oxides, mica

Occurences

Scotland, Australia, Ontario (USA), Alps

Comments

Chert synonyms: silexite, petrosilex, phthanite, hornstone.
These rocks have often been used in prehistoric times as raw material for constructing stone tools. Rocks cannot be scratched with steel knives

Classification

Class

SEDIMENTARY ROCKS

Narrower Terms

agate

chert / flintstone

jasper