Limestones are formed from sediment laid down in sea water or fresh water. Limestone contains calcite, a mineral made from crushed shells and bones of sea creatures. Many of our limestones are dolomitic limestones. This type of limestone is heavier and denser than standard limestone. Although no one is exactly sure how dolomitic limestone formed, it originated from the partial replacement of calcium in limestone by magnesium.
Limestones used in the building industry have three different classifications based on how much one cubic foot of stone weighs:
Low density: 110 - 135 pounds per cubic foot
Medium density: 135 - 160 pounds per cubic foot
High density: 160 or more pounds per cubic foot
Granite is easier in terms of classification. It is an igneous rock having crystals or grains of visible size and consists mainly of quartz, feldspar, and mica or other colored minerals. Whereas other stones have three different classifications, granite used in the building industry has only one. It must be at least 160 pounds per cubic foot and have a water absorption rate of 0.40 percent or less.
QUARTZ BASED SANDSTONE
Quartz-based sandstones include sandstones, quartzitic sandstones, and quartzite.
Sandstone is a sedimentary stone composed mainly of sand-size mineral grains. Most are composed of quartz and/or feldspar, the most common minerals in the Earth’s crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white.
Quartzitic sandstone grains are mainly quartz with silica, a bonding agent that fuses the stone together.
Quartzite is a hard, metamorphic stone which was originally sandstone. Through heating and pressure the quartz sand grains and quartz silica fuse into one.
Factors that distinguish the classification of quartz-based sandstone:
Sandstone: 60 percent minimum free silica content and
135 -150 pounds per cubic foot
Quartzitic Sandstone: 90 percent minimum free silica
content and 150 -160 pounds per cubic foot
Quartzite: 95 percent minimum free silica content and
160 or more pounds per cubic foot