Schungite

(after the village of Shun’ga, Karelian ASSR), a Precambrian rock saturated with carbonaceous (schungite) matter in a noncrystalline state. During metamorphosis, schungites alter to graphitoids and cryptocrystalline graphites.

Unstratified (migrational) schungites, which contain up to 99 percent carbon, occur in the form of blanket veins, crossveins, pockets, and amygdules. They are black and have a strong semimetallic luster. They exhibit a conchoidal fracture. They have a hardness of 3–3.5 on Mohs’ scale and a density of 1,840–1,980 kg/m³. In ash they contain vanadium, nickel, molybdenum, copper, cerium, arsenic, tungsten, and other elements.

Stratified schungites form sheets of different thickness within the volcanogenic and sedimentary strata of Middle Proterozoic age. They are classified according to the mineral base (aluminosilicate, siliceous, and carbonate) or the amount of schungite matter. Schungite rocks with a silicate mineral base are further subdivided into low-carbon schungite rocks (up to 5 percent carbon), medium-carbon schungite rocks (5–25 percent carbon), and high-carbon schungite rocks (25–80 percent carbon).

Schungites are a valuable raw material in construction and industry. Owing to the ability of some schungites to swell during heat treatment, they are used as lightweight aggregate for concrete (schungisite). Their excellent reaction properties (schungites are powerful reducing agents) may be used in the production of yellow phosphorus, iron alloys, and other products. Release agents are manufactured using schungite. Some varieties of schungites are used as decorative building materials.

Industrial deposits of schungites occur in the Lake Onega region of the Karelian ASSR.