Stone and Masonry
In working with stone one should know the various types of stone. There are three main types, given their name from the manner whereby they were formed. Igneous stone is formed when magma from below the earth's crust comes to the surface and solidifies. The liquefied material from beneath the crust of the earth spews forth from a volcano as lava. Basalt is the most common stone to be formed volcanically. It is composed mainly of silica, as is diabase and other primordial stone. Feldspar, which contains aluminum and calcium compounds, is the other common mineral spewed from a volcano.
Metamorphic stones are made from existing materials that have undergone change. As an example, when weathered on the surface, feldspar becomes clay, which can undergo tremendous pressure and become metamorphic slate. Granite is often taken for granted, but comes from quartz and feldspar, sometimes at molten temperatures. It can be either igneous or metamorphic. Most metamorphic rocks have been crushed into their present state by a arent stone upon it. Thus limestone under pressure becomes marble. Quartzite is metamorphic quartz. Gneiss and schist are two other metamorphic rocks.
Sedimentary stones are formed from sediments on the earth's surface. Such stones cover three fourths of the earth's crust, but account for less than five percent of the earth's volume. Shale, sandstone, and limestone make up ninety-nine percent of the sedimentary stone. Shale comes from clay deposits which were formed from feldspar. Sandstone comes from river carried erosion of other stones and minerals that build up at continents' edges. It can also be formed by erosion of igneous stone. Limestone is formed mainly from the buildup of exoskeletons of tiny sea animals drifting to shore. The shell material is mainly calcium carbonate. Limestone is often quarried for building stone, gravel, cement or agricultural lime. Weathered stone supplies the minerals that plants and animals need for their existence.