Silicates: humites
Diagnostic Card.
On the picture. For typical humite crystallization in the form of granules (top); as well crystallized minerals of its group (the bottom - a sample clinohumite).
7 Mg (OH, F) 2 (SiO 4)3
Crystal system orthorhombic
Hardness 6-6.5
The proportion of 3.1-3.2
Cleavage is poor
The color white, yellow, brown
The color in the gray-white powder
Gloss glass
Humites occurs as rounded grains of gray-white, yellowish or light brown with a glassy luster, sometimes passing in the resin.
Theor. composition 3Mg2SiO4-Mg (Fl, 2H0,8): MgO - 58,46, SiO2 - 37,32, F - 4,72, H2O-1,48. Fluctuations in the composition depend on the content of isomorphic impurities Fe2 +, Mn2 +, Ti4 +. The Features. recovered. Rounded grains and aggregates. Well-formed crystals are rare. The size of the individual grains and crystals typically 2-10 mm. The structure. and morph, Kristen. Rombo-dipyramids. Cl. D2h - mmm (3L33PC); a: b: c = 2.1605 1: 4.4013. The crystals are less rich in faces, than the crystals and chondrodite clinohumite. Typically, with well developed faces (001) and (OUT), e (114) C (013) and faces the belt [010]. Some crystals tolstotablitchatye, flattened on (001). There are doubles and tees on the (607) and (207) (adopted in the installation) - faces such crystals have been observed; common cross-shaped germination individuals. Cn. at (001) imperfect.
In thin sections of yellow or colorless rounded grains, usually without crystallographic contours and cleavage. Pleochroic: by Ng - colorless, for Nm - colorless, pale yellow, for Np - yellow, dark yellow. Biaxial (+). Pl. wholesale. axes (001), Ng = b, Nm = s. The refractive indices depend on the isomorphic replacements Mg on Fe2 + and Ti4 +, OH on F; dispersion is very weak.
Diagnostic features.
Under the influence of hydrochloric acid released gelatinous precipitate; in the flame of a candle does not melt. P. p. Tr. It is white, melted with great difficulty. With phosphoric salt gives reaction to F. With cobalt nitrate solution acquires a pink color (if does not contain a lot of iron).
Origin.
Usually associated with Scarpa.
Place of Birth.
Humites found in volcanic emissions of Monte Somma, in limestone Los Llanos de Hanuar in Andalusia (Spain) and limestone Pargas in Finland. Marked in Filipstadte in Sweden and in Brewster in New York State. Group humite. Humites part of the group (called group humite), which owns a number of rare minerals with a collector or scientific interest.
Chondrodite - Mg5 (OH, F) 2 (SiO4). Presented prismatic small crystals with a lot of faces, but more rounded granules (as well as egg-shaped or irregular) shape, with a glass-resin luster; color yellow or light brown-red. Present in limestones and dolomites, changed during the contact metamorphism. In Italy, found in products of volcanic limestone structure in Monte Somma to Vesuvius.
Clinohumite - Mgg (OH, F) 2 (SiO4) 4. It crystallizes in the form of irregular granules yellow or light brown-red color. Formed in the process of metamorphism at the contact of igneous rocks and limestone. It occurs in association with humites in volcano Monte Somma emissions and in some parts of Finland, Sweden and the United States.
Titanklinogumit - Mg8Ti (OH) 2 (SiO4) 4. It is also called titanolivinom and is considered as the difference besftoristuyu clinohumite containing 2-3% titanium oxide. It forms irregular crystals and beads with a resin-but-glass shine and a light red color. Present in the peridotites and serpentinites. There has also been some limestones. Meetings in serpentinized peridotite in Valle di Susa, Val d'Allos, Val d'Aosta and the Val Malenko. This mineral is marked near the Volta region in Liguria. In association with garnet, pyroxene and brucite it is detected in the zone of contact lenses of magnetite, limestone and serpentinite in Monte Creil near the city of Konya in the Val d'Aosta.
Clinohumite. Kuhilal, SW Pamir, Tajikistan. Photo: © AA Evseev.
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