Short answers, pulled from the story.
A gemstone is a piece of mineral crystal that is cut or polished to make jewelry or other adornments. Certain rocks such as lapis lazuli, opal and obsidian, and organic materials such as amber, jet and pearl, are also often considered gemstones.
In modern use the precious stones are emerald, ruby, sapphire and diamond, with all other gemstones classified as semi-precious. These four are translucent, hold fine color in their purest forms, and rate a hardness of 8 to 10 on the Mohs scale.
The colored gemstone industry, meaning everything other than diamonds, is currently estimated at US$1.55 billion. It is projected to increase to a value of $4.46 billion by 2033.
The four Cs stand for color, cut, clarity and carats, and were introduced to describe how a diamond is graded. In diamonds the cut is the primary determinant of value, followed by clarity and color, while for colored stones the purity and beauty of the color is the primary determinant of quality.
Synthetic gemstones are created in a laboratory and are physically, optically and chemically identical to natural stones. Common methods include the Verneuil flame fusion process, the Czochralski crystal pulling method, flux growth and hydrothermal growth.
Auguste Verneuil developed the flame-fusion process in 1902. Ruby was the first gemstone synthesized through it, and the method remains the most cost-effective way to make corundum, reaching world production of 1000 million carats a year.
A gemologist is a gem expert who identifies and describes gemstones. A lapidarist or gemcutter is a gem maker, while a diamantaire is specifically a diamond cutter.
Color comes from impurities in the atomic structure that absorb certain wavelengths of light and reflect others. Pure beryl is colorless, but it becomes emerald with chromium, pink morganite with manganese, and aquamarine with iron.