Building Stones

Stones used in building can be divided into three classes:

• igneous
• sedimentary
• metamorphic

Igneous Stones

These stones originate from volcanic action, being formed by the crystallization of molten rock matter derived from deep in the earth's crust. It is the proportions of these crystals that give the stones their colour and characteristics. Granites are typical of this class of stone, being hard, durable, and capable of a fine, polished finish.Granites are composed mainly of quartz, feldspar and mica.

 igneous rock

Sedimentary Stones

 These stones are composed largely of materials derived from the breakdown and erosion of existing rocks deposited in layers under the waters that, at that time, covered much of the earth's surface. Being deposited in this manner, their section is stratified, and shows to a lesser or greater degree the layers as deposited. Some of these layers are visible only if viewed under a microscope. Sandstones and limestones are typical examples of sedimentary stones.

   Sandstones are stratified sedimentary rocks produced by eroded and disintegrated rocks such as granite, being carried away and deposited by water in layers. The brown and yellow tints in sandstones are due to the presence of oxides of iron.

 sandstone

  

Limestones may be organically formed by the deposit of tiny shells and calcareous(containing limestone) skeletons in the sea and rivers, or they may be formed chemically by deposits of lime in ranged layers. Limestones vary considerably, from a heavy crystalline form to a friable material such as chalk.

 limestone

Metamorphic Stones

These are stones that have altered and may have been originally igneous or sedimentary rocks, but have since been changed by geological processes such as pressure, movement, heat and chemical reaction due to the infiltration of fluids. Typical examples of this type of stone are marbles and slates.

   Marbles are metamorphic limestones, their original structure having been changed by pressure. Marbles, being capable of taking a high polish, are used mainly for decorative work.

 marble

   Slate is a metamorphic clay, having been subjected to great pressure and heat; being derived from a sedimentary layer it can be easily split into thin members. Stones areobtained from quarries by blasting and wedging the blocks away from the solid mass. They are partly worked in the quarry and then sent to store yards, where they can be sawn, cut, moulded, dresses and polished to the customer's requirements.

  slate

Today, natural stones are sometimes used for facing prestige buildings, constructing boundary or similar walls and in those areas where natural stones occur, to reserve the character of the district.