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chert / flintstone

chert / flintstone

SRI Petrography ID: 63

Names

[de] Feuerstein
[en] chert / flintstone

Description

Chert is a hard, dense sedimentary rock that is composed of microcrystalline, cryptocrystalline and microfibrous quartz (SiO2). It is characterized by a semivitreous to dull luster and characteristical splintery to conchoidal fracture.
Chert occurs in three forms:
Nodular
massive
bedded

While “chert” refers to all rocks composed primarily of microcrystalline, cryptocrystalline and microfibrous quartz (NOT: quartzite),"flint" means a variety of chert occuring in nodules in chalk and marly limestones. In archaeology the two terms are used similarily, mostly referring to a quality difference: usually the term “chert” is used for lower quality material than “flint”.
Chert is mostly grey, black, brown, red or green in colour due to impurities (traces of iron oxides, manganese oxides, clay minerals).
Another variety of “chert” is “jasper”: typically for jasper is the red or yellow colour, due to contents of varying iron ore or oxides.

Color

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

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

Most important chert varieties: flint (black), jasper (red or brown), radiolarite (redbrown, brown, yellow, greenish),
Achate, onyx, chalcedony, opal derive from thermal origin and were associated with volcanic rocks.
Chert synonyms: silexite, petrosilex, phthanite, hornstone.
Chert and its varieties have often been used in prehistoric times as raw material for constructing stone tools.

Classification

Class

SEDIMENTARY ROCKS

Broader Terms

non clastic silica-rich sedimentary rocks