Short answers, pulled from the story.
Granite is a coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, mica, and plagioclase. True granite contains between 20% and 60% quartz by volume, with alkali feldspar making up 35% to 90% of the total feldspar. It forms from silica-rich magma that cools and solidifies slowly underground.
Granite falls around 6.5 on the Mohs hardness scale. It is also nearly always massive and tough, with an average density between 2.65 and 2.75 g/cm3 and a compressive strength usually above 200 MPa. These properties have made it a widespread construction stone throughout human history.
These are categories in the letter-based Chappell and White classification, based on a granite's parental rock. I-type granites are high in sodium and calcium with a strontium isotope ratio below 0.708 and are known for porphyry copper deposits. S-type granites are sodium-poor, aluminum-rich, and host tin ores, while A-type granites form over hot spots and continental rifting with high silicon and potassium.
Granite is a natural source of radiation, carrying potassium-40 and, in some cases, around 10 to 20 parts per million of uranium. The decay of that uranium produces radon gas, which can collect in cellars and basements built over granite. Radon is the number two cause of lung cancer in the US behind smoking, though a 2008 study of 39 granite slabs found radiation well below European Union safety standards.
In Ancient Egypt granite was used for sarcophagi, columns, door lintels, sills, jambs, and wall and floor veneer. The Great Pyramid of Giza, dating to around 2580 BC, contains a granite sarcophagus made of Red Aswan Granite, and the Black Pyramid of Amenemhat III once had a polished granite pyramidion. Granite and related marble industries are considered among the oldest industries in the world.
Curling stones are traditionally fashioned of Ailsa Craig granite, first made in the 1750s from the island of Ailsa Craig in Scotland. Because the granite is rare, the best stones can cost as much as US$1,500, and between 60 and 70 percent of stones used today come from this source. The island is now a wildlife reserve but is still quarried under license by Kays of Scotland.
Granitic rock is widely distributed throughout the continental crust and is the most abundant basement rock beneath the continents. Much of it was intruded during the Precambrian age and appears as tors, domes, bornhardts, batholiths, and smaller stock masses. Major modern exporters of granite include China, India, Italy, Brazil, Canada, Germany, Sweden, Spain, and the United States.