#gemstone
- Aquamarine — A transparent variety of beryl, light blue, greenish-blue, or turquoise in color, highly valued as a gemstone in jewelry; it also designates a chromatic shade mimicking the color of sea water. The structural properties of this crystal are determined by trace amounts of iron within its atomic lattice, granting it exceptional clarity and unique light reflections.
- Agate — A microcrystalline variety of quartz, representing a form of chalcedony that is structurally characterized by concentric or parallel bands of different colors and opacities arranged in successive layers. Geologically, it forms within the cavities of volcanic rocks (geodes) through the rhythmic deposition of silica from hydrothermal solutions, being widely used in crafting decorative objects, luxury jewelry, and as precision bearings in mechanics.
- Agate — An alternative, less frequent, or archaic spelling and phonetic form for the mineral widely known as agate. It represents a microcrystalline variety of quartz (chalcedony), characterized by successive layers of different colors and distinct banded textures, extensively used in jewelry making, luxury decorative objects, and precision manufacturing due to its high hardness.
- Agates — The plural form for the mineral ahat (agate). It designates multiple pieces, specimens, or striped varieties of chalcedony. In old specialized texts or archaic museum catalogs, the term is used to classify collections of semi-precious stones characterized by diversely colored bands and alternating opacities.
- 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.
- Almandine — A silicate mineral representing the most widespread and common species of the garnet group, featuring a characteristic deep red, purplish-red, reddish-brown, or black color, containing iron and aluminum. It crystallizes in the cubic system, has a vitreous luster, and high hardness (7-7.5 on the Mohs scale), with its transparent varieties utilized since antiquity as semi-precious gemstones in jewelry and opaque ones as industrial abrasives.
- Almas — A term borrowed from Oriental languages (from Turkish or Arabic - 'almas' / 'almás') historically or comparatively used to denote a diamond or a gemstone of exceptional hardness and brilliance; in geography, it represents a spelling variant without diacritics for 'Almaș', a river and historical region in Transylvania (Romania), rich in archaeological remains and folklore traditions.
- Amazonite — A green to bluish-green variety of microcline feldspar, crystallizing in the triclinic system, widely used as a semi-precious ornamental gemstone. Its unique color and vitreous luster are structurally caused by microscopic trace amounts of lead and water within the crystal lattice.
- Andradite — A mineral belonging to the silicate group and the garnet subgroup, chemically composed of calcium iron silicate. This structural mineral occurs in metamorphic rocks (especially skarns and crystalline limestones) and crystallizes in dodecahedral or trapezohedral forms with shades of yellow, green, brown, or black, being highly valued in its rare varieties (such as demantoid and melanite) as a gemstone.
- Aventurine — A microcrystalline variety of quartz or feldspar, shiny and opaque, characterized by the presence of tiny inclusions of mica, hematite, or chlorite, which reflect light and produce a glittering effect called aventurescence; additionally, the term denotes a special artificial glass invented in Murano containing microscopic crystals of metallic copper. As an adjective, it describes a texture, a reddish-brown color, or an object presenting glittering metallic reflections similar to this mineral.
- Aventurine stone — A feminine variant used in the commercial jargon of jewelers and in practical gemology to denote the semi-precious stone aventurine, praised for its aesthetic and decorative properties; it refers specifically to pieces polished as cabochons or beads used in manufacturing necklaces, amulets, and ornaments. In lithotherapy, the term is traditionally associated with emotional balance, luck, and prosperity.