Gemology is not only concerned with the study of gem materials, but also gem testing and evaluation methods, cutting and polishing, synthetically manufactured gems, precious metals and alloys, grading, marketing, and sales. Gemstone Gemstone is a collective term for all objects used with ornamental stones for personal adornment that possesses beauty, durability, and stability. Durability is the resistance of the gemstone damage and dependent upon physical properties, such as hardness and tenacity. Tenacity is the resistance to bending and breaking, while hardness measures the resistance to scratch. Nephrite jade is relatively soft for a gem, easily scratched by dust in the air, but it is composed of fibrous crystals that resist breaking and therefore, it is tough or has high tenacity.
Stability refers to the gem's ability to retain color inspite of heat, light, or chemical assaults.
The rare gem, or one with limited available quantities, is considered desirable by those who can possess it. Rarity can lead to increased demand and prices, which can lead to new discoveries that will bring down the price. Demand and gem value fluctuate with current fads or fashion. Dark red garnets from Bohemia were very popular in the nineteenth century, but these jewelry pieces are not in demand today. Amber and turquoise jewelry was popular at the beginning of the twentieth century, fell out of favor, and has experienced a resurgance of popularity at the end of this century.