#gemology
- Alexandrite — A rare and highly valuable variety of chrysoberyl (beryllium aluminate) containing traces of chromium, characterized by the remarkable property of changing color depending on the lighting conditions (pleochroism). The gemstone appears emerald-green or bluish-green in natural daylight and shifts to raspberry-red, purplish, or violet under incandescent artificial light.
- Amethyst — A violet, purple, or lilac semi-precious macrocrystalline variety of quartz, whose coloration is due to iron and titanium impurities combined with natural irradiation within its trigonal crystalline structure. This structural mineral is widely utilized in jewelry, high-end decorative crafts, and is valued in crystal healing for its symbolic calming properties.
- Asteria — A variety of precious gemstone (especially sapphire or ruby) which, due to fine acicular rutile inclusions in its structure, exhibits the optical phenomenon of asterism (a luminous six- or twelve-rayed star visible upon light reflection); in a historical zoological sense, it represents an ancient genus or reference to fossil starfish or marine radiate organisms of the Asteroidea class.
- Asterism — A remarkable optical phenomenon found in certain crystals and gemstones (such as star sapphires or star rubies), manifested by a star-shaped light reflection with multiple rays, caused by light refraction on geometrically oriented micro-inclusions; in astronomy, it denotes a small group of stars forming a recognized geometric figure in the night sky that is not an official constellation; in typography, it represents a group of three asterisks (⁂) used to separate text sections.