Chert
A species of Sedimentary, Also known as Chirt Scientific name : Chert RockType : Sedimentary
Chert, A species of Sedimentary
Also known as:
Chirt
Scientific name: Chert
RockType: Sedimentary
Photo By James St. John , used under CC-BY-2.0 /Cropped and compressed from original 
Description
Chert is a very hard sedimentary rock composed of tiny quarts crystals. Though it has few uses today, this material was invaluable to paleolithic humans. Hard and able to keep a sharp edge when knapped, chert was commonly used for arrowheads, knives, scrapers, and other tools. It also creates sparks when struck against steel, and so it was used as a firestarter, and later as a component in flintlock firearms.
Physical Properties
Colors
Gray, white, black, brown
Texture
NonClastic
Chemical Properties
People often ask
General Info
How to Select
When considering chert, a type of sedimentary rock, several characteristics can make certain varieties more desirable:
1.Color: chert comes in various colors, including white, red, brown, green, gray, and black. Chert with more vivid and beautiful colors is generally more attractive.
2.Translucency: Certain types of chert, when sliced thin, reveal a degree of translucency that can be quite beautiful and sought after by collectors and artisans alike.
3.Purity: Chemically pure chert, free from impurities, is desirable due to its uniform texture and color.
4.Pattern and Inclusions: chert with unique patterns or fossil inclusions can be highly desirable for collectors.
5.Fracture Quality: chert that exhibits conchoidal (shell-like) fractures is particularly valued, especially in flintknapping for the creation of tools or weapons.
6.Nodules and Beds: chert nodules (rounded masses) and bedded chert (layers within other rocks) are often sought after in geological studies and collecting.
The desirability of certain qualities or varieties of chert largely depends on its intended use and the preferences of the individual collector or user.
Usage
Chert was once a popular stone for creating blades and weapons because it is hard and has a very particular fracture pattern. However, in the modern day it is more often used as an aggregate material for construction, though it is not the most popular choice as it can crack easily.
Types
There are numerous varieties of chert, classified based on their visible, microscopic and physical characteristics. Some of the more common varieties are:
- Flint is a compact microcrystalline quartz. It was originally the name for chert found in chalk or marly limestone formations formed by a replacement of calcium carbonate with silica. Commonly found as nodules, this variety was often used in past times to make bladed tools. Today, some geologists refer to any dark gray to black chert as flint.
- "Common chert" is a variety of chert which forms in limestone formations by replacement of calcium carbonate with silica. This is the most abundantly found variety of chert. It is generally considered to be less attractive for producing gem stones and bladed tools than flint.
- Jasper is a variety of chert formed as primary deposits, found in or in connection with magmatic formations which owes its red color to iron(III) inclusions. Jasper frequently also occurs in black, yellow or even green (depending on the type of iron it contains). Jasper is usually opaque to near opaque.
- Radiolarite is a variety of chert formed as primary deposits and containing radiolarian microfossils.
- Chalcedony is a microfibrous quartz.
- Agate is distinctly banded chalcedony with successive layers differing in color or value.
- Onyx is a banded agate with layers in parallel lines, often black and white.
- Opal is a hydrated silicon dioxide. It is often of a Neogenic origin. In fact it is not a mineral (it is a mineraloid) and it is generally not considered a variety of chert, although some varieties of opal (opal-C and opal-CT) are microcrystalline and contain much less water (sometime none). Often people without petrological training confuse opal with chert due to similar visible and physical characteristics.
- Magadi-type chert is a variety that forms from a sodium silicate precursor in highly alkaline lakes such as Lake Magadi in Kenya.
- Porcelanite is a term used for fine-grained siliceous rocks with a texture and a fracture resembling those of unglazed porcelain.
- Tripolitic chert (or tripoli) is a light-colored porous friable siliceous (largely chalcedonic) sedimentary rock, which results from the weathering (decalcification) of chert or siliceous limestone.
- Siliceous sinter is porous, low-density, light-colored siliceous rock deposited by waters of hot springs and geysers.
- Mozarkite a varicolored, easily polished Ordovician chert that takes a high polish. It is the state rock of Missouri.
How to identify it?
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