Salt Data

<bibimport/> Author:Hans-Jürgen Schwarz
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Abstract

All necessary data, graphics and images for the identification and characterization of a salt are presented. The structure of the salt systems is subject to the major anions.

The Salts

Here you will find a general overview of the salts. If you need detail information, please go to the pages of the individual salts. Recent reviews on salt and salt damage can be found at [Leitner.etal:2003]Title: Mauersalze und Architekturoberflächen
and [Steiger.etal:2007]Title: Special issue on salt decay

Carbonates

The carbonates are salts of the "carbonic acid"(H ₂ CO ₃ ). The main structural element is the planar complex anion [CO ₃ ] ^{2 -} . The carbonates have a number of characteristics that distinguish them well from other minerals / salts. The most important characteristic is that they all decompose more or less easily under CO ₂ when treated with acids. The alkali and alkali earth carbonate salts are colourless. Most of the other carbonates are usually coloured pale, only the heavy metal carbonates can show strong colours (such as azurite). Noteworthy is the extremely high birefringence of the carbonates, which leads to higher order interference colours. Under thermal treatment the carbonates dissociate mostly at temperatures between 500-900 °C. The solubility in water is relatively good, especially in carbonated water.

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Nitrates

Biogenic reactions are a major source of nitrates with the [NO ₃] ^- ion . This usually takes place with the help of bacteria, also nitrogen-containing raw materials such as animal waste, manure and other organic substances may play a role. Nearly all nitrates are soluble in water. The nitrates have remarkable structural similarities with the carbonates; characteristic is the isotypy (same crystal structure) between nitronatrite /calcite and aragonite /niter.

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Sulphates

Sulfates are compounds with the divalent anion [SO₄]^2-. The sulfate anion is formed in nature by the oxidation of sulfur or sulfur compounds, especially the sulphides. In many cases, microorganisms (eg, Thio - or sulfur bacteria) are involved in this process. A large proportion of atmospheric sulfate and their precursors (e.g. sulfur dioxide SO ₂) is anthropogenic and is produced by combustion processes. The relatively large [SO₄] - complex forms stable pure compounds only with large divalent cations such as barium. The smaller the bound ions are, the more unstable are the sulfates, and the more they are forced to stabilize themselves by addition or incorporation of H₂O. Therefore, most sulfates, especially the one-and three valent elements contain water or have additional anions such as [OH], [CO₃] and others The sulphates have a number of common characteristics. All sulfates here considered are colourless. The optical birefringence is usually lower than in the carbonates and nitrates. A very large part of the complex salts is slightly to very soluble in water.

to the Sulfates

Chlorides

The chlorides of the alkali and alkaline earth metals are all pronounced ionare compounds. Since the cations have a low charge and a relatively large ionic radius, their polarizing effect is small on the chloride ions. The result is that these minerals are usually colorless and transparent. Other common features are the low refractive index and low density. The chlorides, especially those of the alkalis are very soluble in water. In contrast, the fluorides are sparingly soluble. This is due to the relatively small size of the fluoride ion (1.33 Å), and thus due to other types of coordination of the fluoride in the crystal lattice.

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More Salts

to the other inorganic salts

Salts with "organic" anions

Salts with organic acid residue anions play in very specific areas a greater role. These are, especially the acetates, which may be in museum showcases a major damaging factor.

Salze mit "organischen" Anionen

Metal Salts

Metallsalze der Übergangsmetalle verursachen aufgrund ihrer Farbigkeit oft eine Verfärbung an Baumaterialien. Ihr wichtigtsen Vorkommen sind jedoch metallische Bauteile, Skulpturen, etc., die aufgrund der Umweltbelastung und durch Reaktion mit in der Atmosphäre enthaltenene Reagenzien zu Salzen führen können. Oft handelt es sich dabei um Carbonate oder Sulfate.

to the metal salts

Literature

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an atom or molecule with a negative electrical charge.

the mathematical difference between the largest and smallest refractive index for an anisotropic mineral

In physics, interference is the addition of two or more waves that results in a new wave pattern. The colours are produced by the difference in speed in the fast and slow rays. Minerals have specific and predictable colours in cross-polarized light, and this can help identify them.