Mineral description : Corundum

Blue to yellow corundum in andesin and surrounded by a rim of margarite. From Södra yxesjön, Värmland.

Mineral class Oxides : Corundum - Spinell - Chrysoberyl group.
Chemical formula Al2O3
Crystal system Hexagonal
Habitus Commonly as short or steep hexagonal crystals, also common as irregular grains or massive.
Cleavage Imperfect, fracture subconchoidal to uneven.
Hardness 9
Density 3.9 - 4.1
Color Usually colorless, yellow, pink, red or blue.
Streak White
Luster Adamantine to vitreous, transparent to translucent.
Description  
Occurance Forms in metamorphic rocks rich on aluminium or in silica poor rocks, as anorthosites and ultrabasic rocks.
Associates Margarite, zoisite, kyanite, gedrite, sillimanite, magnetite.
Notes Ruby is the name of red colored corundum. The red color comes from chromium.
Sapphire is the name of blue corundum.
As corundum is so hard it is often found in placer deposits.
Often transformed into margarite on the surface.
Localities A not so common mineral in Scandinavia.
Sweden : a few localities are known.
  • Malmberget, Lappland. Yellowish gray, up to cm sized crystals and grains in magnetite.
  • Saxberget, Ludvika, Dalarna.
  • Ullared, Falkenberg, Halland.
  • Ulverud, Södra Yxesjön, Eda, Värmland.
  • Persberg, Flipstad, Värmland.
  • Ruoutevare, Jokkmokk, Lappland.
  • Barsevik, Härnösand, Västernorrland.
  • Parvavaara, Gällivare, Lappland.
  • Torsboda, Timrå, Västernorrland.
  • Uggleboda, Karlshamn, Blekinge.
  • Norra Kärr, Jönköping.
  • Arlanda, Norrskogen (3:e banan), Sigtuna, Uppland.
  • Boliden, Västerbotten. In the central zone with an extremely leached zone, leaving aluminium rich minerals as andalusite.
Norway : a number of localities are known.
  • Sagstuen, Farsjö, Årnes.
  • Froland, Arendal. As deep red short prismatic crystals in schist, up to 10 cm wide but only 1 cm high.
  • Vestpolltind, Hinnöy, Lofoten.
  • Rausand. Crystals up to 1.5 mm in the titane-iron ore.
  • Breivikbotn, Söröy, Vest-Finnmark. In nefelinesyenite rocks.
  • Bergens field. In anorthosite gabbros. As black irregular grains up to 0.5 mm.
  • Seljenes, Nordpoll, Selje. In nodules in an ecologite together with margarite.
  • Stadtlandet and Almklovdalen, Nordfjord. Corundum appears as a transformation zone around kyanite together with oligoclase.
  • Lyngen area. As veins in tremolite - carbonatite - orthopyroxenite rocks, together with spinel, up to 5 cm wide.
  • Kallskaret, Tafjord area. In the Vikvatn sequence, in ultra mafitic rocks near dunites. As porfyroblasts in coarse schist up to 2 cm.
  • South Kallskaret, Tafjord area. In an anothositic layer, close to a dunite, with an extreme coarse grained corundum, up to 15-20 cm crystals. Associated minerals are margarite and chlorite.
  • Kongsfjell area, Bleikvatnet, south Mo i Rana. In a zone between soapstone and amfibolite. As hexagonal white to clear prismas up to a cm, somewhat corroded. Some with a deep blue or red core.
Finland : Some localities exists, but this is all information I have.
  • Espoo, Vantaa, Helsinki, Uusimaa, Southern Finland. With amethyst and chrysoberyl.
  • Isola, Miessijoki, Inari, Lappi Province. As placer deposit.
  • Kaarreoja, Lemmenjoki, Inari, Lappi Province. As placer deposit.
  • Puskuoja, Lemmenjoki, Inari, Lappi Province. As placer deposit.
  • Paaraskalla, Kittilä, Lappi Province. With kornerupine, gedrite and hornblende.

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Last changed : 2000-10-15