The rocks in the earth’s crust are magmatic, sedimentary and metamorphic. The magmatic ones are either intrusive, or effusive, where the intrusive ones are formed when the magma solidifies in the crust, and the effusive ones are formed when the lava gushes out on the surface.

Mohs Scale

Hardness in Moos Mineral Absolute hardness
1 Talc (Mg3Si4O10(OH)2) 1
2 Gypsum (CaSO4·2H2O) 3
3 Calcite (CaCO3) 9
4 Fluorite (CaF2) 21
5 Apatite (Ca5(PO4)3(OH-,Cl-,F-)) 48
6 Orthoclase (KAlSi3O8) 72
7 Quartz (SiO2) 100
8 Topaz (Al2SiO4(OH-,F-)2) 200
9 Corundum (Al2O3) 400
10 Diamond (C) 1600

Sediment rocks

  • Limestone
  • Sandstone
  • Travertine, etc.


  • Marble
  • Gneiss


Marble (from the Greek word for sparkling, marmaros) is a grainy crystalline material formed in the recrystallization of limestone and dolomite at high temperatures and under high pressure, resulting in a crystal structure of various colours and patterns.
The marble found at the Ilindentsi Field is mostly decorative types И1-2, И3-4 and И6.

  • И1-2 – Snow-white types of marble. They are strong, dense, and solid; mostly fine or medium crystalline.
  • И3-4 – Light grey, grey to dark grey types of marble. Exceptionally strong, dense and solid.
  • И6 – Snow-white types of marble. They are solid; fine to medium crystalline.
Decorative type Density, g/cm3 Specific density, g/cm3 General porosity, % Compressive strength, air dry state, Mpa Frost resistance ratio Tensile strength, air dry state, Mpa Deval abrasion test, %
И3-4 2,66 2,73 2,44 91,4 0,87 9,5 3