Flint

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

Notes

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

Links

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
URLs	http://en.wikipedia.org/wiki/Flint Flint on Wikipedia
URLs	http://www.mindat.org/min-6676.html Flint at Mindat.org

By Tony Hansen
Follow me on

Got a Question?

Buy me a coffee and we can talk