Natural stones exist in numerous varieties, each with its own texture, color, hardness, and chemical composition. Some of these varieties are hard, rugged, acid resistant, and slow to erosion. Other varieties are softer, erode quickly, and are vulnerable to acid attacks. Let us study these varieties one by one:

Granite
Granite is one of the most popular natural stones. It is an igneous rock composed of alkali feldspar, quartz, and plagioclase. Granite and marble have existed since ancient civilizations as far back as Ancient Egypt.

Characteristics

• Granite is considered very hard, tough, and abrasion-resistant, with a more compressed natural bedding plane than other natural stones like marble.
•  Visually, granite has a coarse-grained appearance.
• Average density: 2.65 to 2.75 g/cm3
• Compressive Strength: 200 MPa 
• Melting temperature: 1215 to 1260 °C at ambient pressure
• Poor primary permeability (ability to allow the water to pass through pores)
• Strong secondary permeability in cracks
   

Quartzite
Quartzite is a metamorphic rock formed when heat and pressure are applied to quartz sandstone under the Earth’s surface. Quartzite is naturally dark gray in color. However, it often has an infusion of hematite resulting in various shades of red and pink colors. Other mineral infusions can also result in shades of yellow, green, and blue.

Characteristics

1. Quartzite is very hard due to the interlocked quartz crystals inside it. 
2. It is harder than granite and has better stain resistance.
3. Average Density: 2.6 to 2.8 g/cm3
4. Compressive Strength: Around 300 MPa
5. Melting Temperature: 1350 to 1500 °C
6. Quartzite can be permeable or non-permeable, depending on the degree of heat and pressure it has undergone during its formation.
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Marble
Marble is one of the most popular all-natural stones. It is a metamorphic rock made under the Earth’s surface by the transformation of limestone. It consists mainly of carbonate minerals such as dolomite or calcite.

Characteristics

• Hardness: 2 to 3. 
• Density: 1.9 to 2.8 g/cm3
• Compressive Strength: 30 to 210 MPa
• Melting Point: 825 °C
• Marble is porous but impermeable.