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activity coefficient

Overview page. Subjects: Earth Sciences and Geography — Chemistry.

The ratio of chemical activity (i.e. the effective concentration, a) of a component in a solution, to the actual mole fraction (X) present in solution: (γ = a/X). Values for activities are...

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anhydrite

Overview page. Subjects: Earth Sciences and Geography — Chemistry.

An important rock-forming anhydrous mineral form of calcium sulphate, CaSO4. It is chemically similar to gypsum but is harder and heavier and crystallizes in the rhombic form (gypsum is...

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argentite

Overview page. Subjects: Earth Sciences and Geography — Chemistry.

A sulphide ore of silver, Ag2S. It crystallizes in the cubic system but most commonly occurs in massive form. It is dull grey-black in colour but bright when first cut and occurs in veins...

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argon

Overview page. Subjects: Meteorology and Climatology — Chemistry.

A natural, colourless, odourless, inertgas that is the third most abundant constituent of dry air (it comprises 0.93% of the Earth's atmosphere).

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barometric pressure

Overview page. Subjects: Chemistry — Meteorology and Climatology.

The pressure exerted by the atmosphere at a given place and time. It is often expressed in terms of the supported height of a column of mercury, usually measured in ...

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bornite

Overview page. Subjects: Earth Sciences and Geography — Chemistry.

An important ore of copper composed of a mixed copper-iron sulphide, Cu5FeS4. Freshly exposed surfaces of the mineral are a metallic reddish-brown but a purplish iridescent tarnish soon...

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carnotite

Overview page. Subjects: Earth Sciences and Geography — Chemistry.

A radioactive mineral consisting of hydrated uranium potassium vanadate, K2(UO2)2(VO4)2.nH2O. It varies in colour from bright yellow to lemon- or greenish-yellow. It is a source of uranium,...

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case hardening

Overview page. Subjects: Earth Sciences and Geography — Chemistry.

The hardening of the surface layer of steel, used for tools and certain mechanical components. The commonest method is to carburize the surface layer by heating the metal in a hydrocarbon...

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cerussite

Overview page. Subjects: Earth Sciences and Geography — Chemistry.

An ore of lead consisting of lead carbonate, PbCO3. It is usually of secondary origin, formed by the weathering of galena. Pure cerussite is white but the mineral may be grey due to the...

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chlorite

Overview page. Subjects: Earth Sciences and Geography — Chemistry.

Important group of phyllosilicate (sheet silicate) minerals with the general composition (Mg,Fe,Al)6[(SiAl)4O10](OH)8 and related to the micas; sp. gr. 2.6–3.3; soft and green; platy or...

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