Short answers, pulled from the story.
Granite is a coarse-grained igneous rock that forms from silica-rich magmas cooling slowly underground over millions of years. It is composed primarily of quartz, alkali feldspar, and mica, creating an interlocking matrix of visible crystals.
Humanity has used granite for thousands of years, with the Red Pyramid of Egypt dating back to around 2580 BC utilizing granite blocks. The Egyptians quarried granite for columns, door lintels, and wall veneers using tools made of flint and possibly emery.
The best granite for curling stones is quarried from the rare Ailsa Craig in Scotland. These stones cost as much as US$1,500 and are chosen for their durability and resistance to wear.
Granite is a natural source of radiation containing potassium-40 and varying amounts of uranium and thorium. This composition can lead to the accumulation of radon gas in cellars and basements, which is the number two cause of lung cancer in the United States behind smoking.
Granite falls between 6 and 7 on the Mohs hardness scale, making it one of the hardest natural materials available. Its chemical composition includes between 20% and 60% quartz by volume, contributing to its toughness.