Glance or glances (German: glanz, glanze), sometimes also galenoids (similar to galena) — obsolete or partially obsolete collective name for the morphological group of minerals, compiled according to external characteristics. The group included more than three dozen names, mainly from the group of sulfides and related compounds. As a rule, different examples of glosses have a gray mirror or metallic luster with refractive indices above 3, and sometimes a metallike appearance. Unlike the related pyrites or blendes, glosses are not considered ″colored″ because they do not have the yellowish or reddish ″copper″ tones, although impurities may well give individual varieties shades of color. The group of glances was formed spontaneously by miners and mining practitioners, but mineralogy as a science recognized this group until the mid-twentieth century. However, even in the 17th-19th centuries, at a time when luster or pyrites were considered generally accepted scientific terms, mineralogists treated them without due categorical rigor, understanding them purely broadly as a morphological group united by external characteristics. For example, one of the most famous glances (iron) is not a sulfide, but an iron oxide. With the gradual development of inorganic chemistry and ideas about the structure of minerals, the group of shines lost its meaning, although the old names of minerals, having turned into trivial names, remained in the speech of specialists of various professions: prospecting geologists, miners, artisans, amateurs and collectors of minerals.
Characteristics of the group The group of lusters includes mainly sulfides of heavy and transition metals, which have a metallic or mirror-like luster when freshly fractured. The group was composed according to external characteristics, and the most famous minerals of the luster group, by their appearance, immediately give an approximate idea of it. These include: lead glance (galena), copper (chalcocite), antimony (stibnite), molybdenum (molybdenite), as well as cobalt (cobaltine), silver (stephanite) and some others. All of the listed minerals have a metallic glance, dark color and the same feature, low hardness (from 1 to 3, rarely higher). In addition, they attract attention with their increased thermal conductivity (they cool the hand). They all contain sulfide sulfur (S2-) as an anion, sometimes mixed with similar compounds of arsenic or antimony. Most sulfide-type minerals are characterized by a high reflectance (in the range of 50-35%) and, with a few exceptions, appear white or gray in reflected light under a microscope. Most lusters are ore minerals, from which the titular metals included in their composition (in particular, copper, lead, molybdenum, antimony) are isolated on an industrial scale. In the 16th-18th centuries, a group of glances had a utilitarian and, partly, chaotic character. Formed primarily on the basis of the appearance of ores known in Europe, it included many shiny metallic minerals, which miners and miners traditionally called by this word (glances or German: glanz). Knowledge of the chemical composition of these minerals was extremely superficial and could not clarify the most important structural details of their internal structure. As a result, substances that had a clear commonality according to two or three main criteria were brought together into one group:
1) conspicuous metallic (metalloid) appearance, with a characteristic metallic lustre; 2) heavy, giving a color streak, more or less quickly fading or decomposing in the air; 3) easily releasing the metal contained in them and therefore traditionally serving as ores. In full accordance with the properties indicated above, many minerals received special group names from mineralogists already in the 16th–18th centuries. Thus, already at the beginning of the 18th century they were firmly united into visual and recognizable groups of glances, pyrites, etc. The most important role in the interpretation and ordering of the group of sulfide minerals was played by Jöns Jacob Berzelius. In his chemical-mineralogical study of 1843, he hypothesized that sulfur, being, like oxygen, an electronegative element, is capable of forming sulfonic acid bases with electropositive elements, and sulfides (similar to anhydrides) with electronegative ones. Sulfur bases and sulfo bases, when combined with sulfides, give sulfosalts, which in their chemical formula are similar to oxygen salts in which the oxygen atom is replaced by sulfur. Similar to sulfur, selenium and, to a lesser extent, tellurium also have the same ability to replace oxygen in all similar substances. Based on the results of his research, Berzelius combined four elements (the future group of chalcogens: O, S, Se and Te) as corpora amphogenia, that is, on the basis of substances capable of combining with metals to give their compounds the character of bases and acidic oxides. Based on the chemical hypothesis put forward, Berzelius transferred it to the field of mineralogy and created a separate group of sulfur minerals, mainly ore, similar to oxygen compounds. These substances have long been empirically grouped together by miners and practicing geologists on the basis of outward physical characteristics only, without any reference to their structure or chemical formula. The fact that Berzelius's new theory agreed in general terms with the traditional classification of mineralogists seemed to indicate that the classification of these minerals into one or more closely related groups was, in general, correct.
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