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Description: Silica

Oxide Analysis Formula
CaO 3.00% 0.03
SiO2 94.00% 1.00
MgO 0.10% -
Fe2O3 0.10% -
H2O 3.00%n/a
Oxide Weight 62.15
Formula Weight 64.07


Flint, a type of chert generally found in carbonate (sedimentary) rocks, is a microcrystalline form of silica and has a very different physical appearance. The crystals are so tiny that the mineral is opaque and appears glassy or waxy on a broken surface. It has no preferred way of breaking and fractures conchoidally to create knife-sharp edges. Flint appears in nodules or masses within sedimentary bedrock as a primary mineral or secondarily in voids due to silica-rich groundwater (see Wikipedia page). It is common for the flint-containing bedrock to weather and be eroded away leaving the harder, chemically inert flint behind. Flint often has inclusions of various elements including iron and magnesium oxidizes, which can impart banded colorings. There may be inclusions of limestone (thus the CaO content and the LOI). The mineral quartz, on the other hand, forms in igneous or metamorphic rocks as silica cools over long periods of time. This process forms large, visible, crystals with angular structures.

Flint pebbles are employed as grinding media in ball mills (because of their hardness and the fact that rounded pebbles of proper size and low impurity levels can be found in many areas). Historically it was employed as a source of quartz in bodies both because it was more convenient to find and grind into a fine powder (once calcined to 600C flint-stone can be easily crushed). Supposedly it produced bodies less prone to cracking through quartz inversion temperatures.

Today, however, quartz is universally used in bodies and glazes and modern machinery can grind it to any size needed. It is very likey that you have never actually seen real flint powder and will not be able to find the true material from any supplier. The terms "flint", "quartz" and "silica" have come to be used interchangeably in ceramics and you will see them all employed in recipes. However, most correctly, the material used in ceramics is called simply "silica". "Quartz" refers to the macro-crystalline mineral we find in nature. The terms "pottery quartz" or "potter's sand" likewise refer to silica. The term "flint" surfaces most often when referring specifically to the tools ancient peoples made from the micro-crystalline mineral.

Related Information


Materials Silica
Silica, sold as a white powder, is pure quartz mineral. Quartz is pure SiO2 silicon dioxide. It is the most abundant mineral on earth and most used in ceramics.
Materials Flint Pebbles
Typecodes Generic Material
Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Typecodes Silica/Quartz
Quartz is very abundant and there are many grades and name brands.
Typecodes Materials used in Denmark
Flint on Wikipedia
Flint at
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