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What is Natural Stone?

SEDIMENTARY ROCKS are made when pieces of rocks settle from the water or when minerals are deposited by plants, animals, and other chemical processes. [e.g. limestone, sandstone, shale]

METAMORPHIC ROCKS are old rocks that have been squeezed and heated but not melted. What new rock is made depends on what the original rock was and on the amount of heat and pressure. [e.g. gneiss, slate, quartzite, marble]

IGNEOUS INTRUSIVE ROCKS are made when molten rock cools while still underground. [e.g. basalt, granite, gabbro]

IGNEOUS EXTRUSIVE ROCKS are made when molten rock flows on the land surface or is thrown into the air and then is cooled into rock. [e.g. basalt, scoria, tuff] 

- How to Identify Rocks by Bill Langer of USGS

THE ROCK CYCLE: 
All three major rock types can be made into the other type. Rocks are eroded by water, wind, and ice to form sediments. Buried sediments are hardened into sedimentary rocks. If the rocks are buried very deeply they may get heated and squeezed into metamorphic rocks. If rocks get hot enough to melt, they become magma. When magma cools, it forms igneous rocks.

SEDIMENTARY: 
- LIMESTONE is made from shells, coral and calcite; Most mineral scratched with nail
- SANDSTONE is made from sand and you can see the sand grains; Can be picked apart; Not scratched with nail
- SHALE is made from mud and may contain fossils; Very easily split apart; Scratched with nail

METAMORPHIC 
- Limestone can be changed to MARBLE; Can see crystal or veins; Scratched with nail
- Sandstone can be changed to QUARTZITE; Very hard to break; Not scratched with nail
- Shale can be changed into a layered rock called SLATE; Easily split apart; Most minerals scratched with nail
- Many rocks can be changed into a layered rock called GNEISS; Very hard to break; Not scratched with nail

IGNEOUS (EXTRUSIVE) 
- Deposit of hot volcanic ash cool to form TUFF; Very hard to break; Not scratched with nail
- Lava cooled fast and bubbles of gas created holes in SCORIA; Easy to break; Not scratched with nail
- Dark colored very small crystals make BASALT; Very hard to break; Not scratched with nail

IGNEOUS (INTRUSIVE) 
- GRANITE is light colored and has large interlocking crystals; Very hard to break; Most minerals not scratched with nail
- GABBRO is dark colored and has large interlocking crystals; Very hard to break; Most minerals not scratched with nail