Small marble dictionary

Extraction:
operation of extraction of stone material from the quarry, the open air place where there is the material to be extracted. Extraction procedures are different depending on the material.

Hardness:
the resistance of the rock to be engraved or cut, different from the resistance to be broken when bumped (toughness). It depends on the individual components of the rock, on the grain and on the texture. According to their hardness, rocks can be divided into:

• Soft: tuffs and tuffaceous limestones
• Semi-hard: ordinary limestones, soft sandstones
• Hard: crystalline limestones, hard sandstones
• Harsh: granites, porphyries, jaspers

The resistance to wear and tear depends also the hardness of the material that is particularly important for materials used for architectural structures and flooring.

Dressing:
mechanical processing that aims to make the surface smooth and without harshness. Marble is dressed through the mechanical action of abrasive stones. As far as marble slabs are concerned, dressing means smoothing with special cutters to obtain a smooth and semi polished surface.

Polishing:
polishing is the characteristic to provide through specific methods smooth mirror-like surfaces. A rock that can be polished is commonly referred to as marble, although the petrographic meaning of this term is more specific. Polishing increases the shades of colour and the hardness of stones. It is carried out by abrasive wheels with finer and finer grain, then by lead wheels and finally with felt discs to obtain a surface almost perfectly mirror-like.

Marble:
metamorphic rock composed especially by calcium carbonate (CaCO3) whose low index of refraction of calcite allow a special brightness. The typically saccharoidal structure differentiates it from pure limestone. It can have different types of grain and can contain up to 99.5% of calcite. The color varies depending on the accessory mineral. They can be monochrome or polychrome, veined or pure. Compression resistance is around 1000 -1300 Kg/cm2. Commonly the term is used to indicate any rock that can be polished and used for decorations and flooring.

Minerals:
substances in liquid or solid form, physically and chemically homogeneous, organic or inorganic. They originates from the continental drift process: the movements of the earth's crust created faults allowing the outflow from the earth nucleus of homogeneous liquid elements. These ones, later on, came in contact with the outside temperature, solidified and settled in underground mines.

Metamorphic rocks:
rocks formed as a result of a mineralogical and structural reorganization process of preexistent rocks when are subjected to conditions of pressure and temperature different from the original ones. The metamorphic reactions can be considered "crystallization" of new minerals replacing the original ones or their recrystallization.

Vein:
natural or artificial stripe with a different colour compared to the colour of the marble.