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Answer:
When limestone, a sedimentary rock, gets buried deep in the earth for millions of years, the heat and pressure can change it into a metamorphic rock called marble. Marble is strong and can be polished to a beautiful luster. It is widely used for buildings and statues. As you can see from the picture, marble has a very sparkly luster. It occurs in many different colors such as white, pink, gray, red, yellow or black.
Basalt
Basalt is a hard, black volcanic rock. Basalt is the most common rock type in the Earth's crust.
Depending on how it is erupted, basalt can be hard and massive (Figure 1) or crumbly and full of bubbles (Figure 2).
Figure 1.
Figure 2.
Slate
Slate is a metamorphic rock that is formed when shales and clays are put under great pressure and heated inside the earth for millions of years. Like shale, it splits apart into sheets, which means that it has good cleavage. Slate is usually gray or black and is used to make blackboards and roofing tiles.
Limestone
Limestone is a sedimentary rock. It is formed by layers of small pieces of rock and stones pressed hard together. The stone forms in wet areas which mean it will also contain of shells and waste matter from organisms that live in water.Limestone caves are formed when rainwater seeps through cracks in limestone rock and dissolves it. Limestone turns into the metamorphic rock marble when it is subjected to high amounts of pressure and heat.
Uses of limestone
Limestone is important to making cement.
It is used in glass making.
Layers of crushed limestone are placed underneath roads and underneath railroad tracks.
It helps clean drinking water and treat sewage.
Fertilizer used by farmers contains ground up limestone. It is a food for the plants and is good for the soil.
Animal feed also contains some limestone.
Gneiss
Gneiss is a type of metamorphic rock that forms when a sedimentary or igneous rock is exposed to extreme temperatures and pressure. When this happens, virtually no traces of the original rock remain. Gneiss rocks are characterized by their arrangement of minerals into long bands. Gneiss is distinctive among other rocks that have bands because its minerals are not evenly distributed so the bands are various widths.
Answer:
=To dig 324 cubic meters earth in a day, required number of persons =12
=Thus, to dig 270 cubic meters earth in a day, required number of persons = 12×270/324
=270/27=10
=10 person can dig 270 cubic metres.