Quartz and Flint

Flint is a hard and easily split variety of the mineral quartz (composed of silicon dioxide), which occurs not only as flint but also in a wide range of other variehes. Some of these exhibit different colors and colored patterns and have characteristic crystalline structures, while others are amorphous (see Textbox 21). In all its variehes, nevertheless, the hardness of quartz is very high, being graded as 7 on the Mohs scale (see Textbox 23). Almost all variehes are either transparent or translucent and display a distinchve luster. These properties made quartz an attractive material for making ornamental 

Archaeological Chemistry, Second Edition By Zvi Goffer Copyright 2007 John Wiley Sons, Inc. 

When it consists of only silica and water, flint is basically colorless. Impurities within the stone, however, render colored varieties. Thus, much flint is tan, beige, or jet black with a brown homy appearance (the latter color is caused mainly by iron impurities), but there are also gray, pink, and even red varieties. If dark flinf is heated to temperatures above 450°C, the outer layer changes to white. Flint that xmderwent such a heating process is known as burned or calcinated flint, a misnomer probably used because the white surface appears to have changed into lime (Luedtke 1992 Sieveking and Bart 1986). Burned flint is easier to work than is the natural mineral, a property 

Variety Luster Light transmittance Color Other features 

Amethyst Vitreous Transparent or transiucent Purple Banded or uneven 

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Raw Materials. In this first stage, the raw materials are chosen for creating a ceramic product. The type of ceramic product to be created determines the type of raw materials required. Traditional ceramics use natural raw materials, such as clay, sand, quartz, and flint. Advanced ceramics require the use of chemically synthesized powders. 

Coade Stone. A vitreous ware, used for architectural ornament, made in London by Mrs Coade from 1771 until her death in 1796 manufacture finally discontinued in about 1840. The body consisted of a kaolinitic clay, finely ground quartz and flint, and a flux (possibly ground glass). Coated Dolomite Grain. Also known as unfired semi-stable dolomite refractory, this comprises calcined dolomite bonded with tar or oil. 

In the ceramic industry, SiOj is known as sand, silica, quartz and flint. As silica or sand, it is used in the enameling and glass industries, particularly the latter. As ground quartz, or quartz, as it s termed, SiOj is used in some forms of pottery. As ground silica or... 

Silica, Si02, is a hard, rigid network solid that is insoluble in water. It occurs naturally as quartz and as sand, which consists of small fragments of quartz, usually colored golden brown by iron oxide impurities. Some precious and semiprecious stones are impure silica (Fig. 14.36). Flint is silica colored black by carbon impurities. 

Cryptocrystalline forms contain microscopic quartz crystals and include the chalcedony grouping of rocks such as chert, agate, jasper, and flint. 

Section 1.5.5). Quartz is one of the commonest minerals in the earth, occurring as sand on the seashore, as a constituent in granite and flint and, in less pure form, as agate and opal. The silicon atom in all these structures is tetrahedrally coordinated. 

Silica occurs widely in Nature as quartz, often in large transparent crystals of characteristic shape but also in the translucent agglomerations of microscopic crystals known as chalcedony, which includes cherts and flint. Other natural crystalline varieties of Si02 include tridymite and cristobalite (opal is a semiprecious stone that consists of microcrystalline, hydrous cristobalite). All forms of silica involve three-dimensional networks of corner-linked Si04 tetrahedra. 

Fire clays, ball clays, flint clays are kaolinite-rich clays, usually of the 6-axis disordered variety, which contain a relatively high impurity content. Illite, montmoril-lonite, diaspore, boehmite, quartz, and organic material are the minerals usually associated with these deposits. Few, if any, of the kaolinite minerals in these clays have been concentrated enough to afford meaningful chemical data. 

The following raw materials were used for the laboratory reproduction of Egyptian Blue coarse-grained quartz (quartz sand <250 jLm, Pilking-ton Brothers Ltd.) or fine-grained quartz (ground flint <53 JLm, Fulham Pottery Ltd.) calcium carbonate (<53 xm, Analar) malachite (<53 xm) and anhydrous sodium carbonate (<53 xm, Analar). 

Silicon is the second most abundant element in Earth s crust, exceeded only by oxygen. Many rocks and minerals contain silicon. Examples include sand, quartz, clays, flint, amethyst, opal, mica, feldspar, garnet, tourmaline, asbestos, talc, zircon, emerald, and aquamarine. Silicon never occurs as a free element. It is always combined with one or more other elements as a compound. 

Silicon dioxide (silica) exists in two familiar forms in nature quartz, small chips of which occur in sand and flint (Latin fe), an uncrystallized amorphous type of silica. Silica is properly represented as (Si02) because it is a polymeric solid of SiO tetrahedra sharing all oxygens among surrounding tetrahedra (Eigure 13-32c). Eor comparison, solid carbon dioxide (dry ice) consists of discrete 0=C=0 molecules, as does gaseous CO2. 

Boaretto E, Berkovits D, Hass M, Hui SK, Kaufman A, Paul M, Weiner S (2000) Dating of prehistoric caves sediments and flints using °Be and A1 in quartz from Tabun Cave (Israel) Progress report. Nucl InstrMeth Phys Res B 172 767-771... 

Stn. Silica.—This acid is found pure in rock crystal, or in white quartz. Along vrith small and variable quantities of certain metallic oxides it forms many well-known minerals—as yellow or smoke rock crystal with oxide of iron agate, jasper, heliotrope, camelian, with the same metal amethyst with oxide of manganese prase with oxide of nickel rose-quartz with some fugitive colouring matter opal and calcedony with water, c. c. Many sands and sandstones are nearly pure silica, and quartz rock and flint are quite pure. 

Silica occurs in nature as quartzite rock and ganister, both being composed principally of quartz as sand or sandstone also consisting of quartz as flint pebble which is a crypto-crystalline quartz (i.e. the crystals are too small to be seen under the optical microscope but can be detected in other ways) and as chalcedony, opal and agate, which are also crypto-crystalline quartz. 

Resistant minerals such as quartz are common constituents of sedimentary rocks, and some more rare minerals (e.g., garnet, rutile, and zircon) have similar properties. Feldspar is less resistant, but is so common that it is a major constituent of many sedimentary rocks. Precipitated minerals include the carbonates (e.g., calcite and dolomite), sulfates (e.g., gypsum and anhydrite), chlorides, and chalcedonic silica (e.g., chert and flint). 

Aj, = percent acid insoluble residue larger than 45 pm, other than quartz or flint. If a 20% acetic acid is used, dolomite also remains in the residue and thus can be examined. 

A colourless or white vitreous solid, SiOj, insoluble in water and soluble (by reaction) in hydrofluoric acid and in strong allcall m.p. 1713°C b.p. 2230°C. The following forms occur naturally cristoballte (cubic or tetragonal crystals r.d. 232) trldymlte (rhombic r.d. 2.26) quartz (hexagonal r.d. 2.63-2.66) lechatellerlte (r.d. 2.19). Quartz has two modifications a-quartz below 575°C and fi-quartz above 575°C above 870°C fi-quartz is slowly transformed to trldymlte and above 1470°C this is slowly converted to cristo-balite. Various forms of sillcon(IV) oxide occur widely in the earth s cmst yellow sand for example is quartz with iron(III) oxide impurities and flint is essentially amorphous silica. The gemstones amethyst, op, and rock crystal are also forms of quartz. 

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