Glances
| Glances | |
|---|---|
Galena, which gave the group its name | |
| General | |
| Category | Sulfide minerals, galenoides |
| Crystal system | Cubic or cuboctahedral |
| Identification | |
| Color | Lead gray, silvery, metallic white, gray & no specific color |
| Crystal habit | usually cubic or cuboctahedral, blocky, tabular and sometimes skeletal crystals |
| Twinning | Contact, penetration and lamellar |
| Mohs scale hardness | 2-3 (rarely up to 6) |
| Luster | Metallic on cleavage planes |
| Diaphaneity | Opaque |
| Optical properties | Isotropic and opaque |
| Other characteristics | Natural semiconductor |
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.: 10–11 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.: 195
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.: 92
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.