The topaz is a semiprecious gemstone and is used for making ornaments. It occurs in quartz and pegmatite veins.

   Refractories are materials, which can withstand high temperatures without fusing. They are very essential to industries like the metallurgical and ceramic industries wherein high temperature operations are involved.

  The most important refractory minerals are andalusite, bauxite, beryl, chromite, diaspore, dolomite, fire-clay, graphite, kyanite, magnesite, mica schist, monazite, olivine, sillimanite, soapstone, spinel, talc, topaz, tripoli, zircon, quartz, sand, sandstone and quartzite are on display.

  Chromite is a chromium oxide and is the chief ore of chromium. It is black or brownish black in colour and produces a brownish streak by which it is distinguished from magnetite and ilmenite. Its fracture is uneven, sub-metallic to metallic lustre. Its hardness is 5.5 and the specific gravity ranges from 4.1 to 4.9.

Iron Ores

      The economic iron ore minerals are magnetite, hematite, limonite and siderite. All the four types of ores are displayed. The banded hematite with red jasper, hematite from Kurnool, limonite from Salur Taluk and the crystalline siderite from Masulipatnam are some of the interesting specimens. Magnetite quartzite from Kanjamalai, Salem district is also on display.

Banded Hematite

    Hematite is one of the important ores of iron. Since it consists of banded structure it is known as banded hematite. It is steel grey or black in colour and reddish brown streak. Its hardness varies from 5.5 to 6.5 and the specific gravity ranges from 4.9 to 5.3. It contains about 70 percent of iron. India is rich in hematite deposit. One of the world's largest Iron ore deposits is situated in Bihar.

Calcite

     Calcite is chiefly used in the manufacture of cement. Iceland spar is used in the manufacture of optical instruments. Its hardness is 3.