#crystal structure

• Actinolite — A mineral belonging to the monoclinic amphibole group, with the chemical formula Ca2(Mg,Fe)5Si8O22(OH)2, characterized by a dark green or leek-green color. Structurally, it develops as acicular, fibrous, or radiating aggregates, being a common constituent of metamorphic rocks (such as greenschists). Its compact fibrous variety constitutes one of the mineral forms known as asbestos, while the dense microcrystalline variety forms nephrite (a type of jade).
• Actinote — A silicate mineral belonging to the monoclinic amphibole group, synonymous with actinolite, with the chemical formula Ca2(Mg,Fe)5Si8O22(OH)2. It occurs structurally as long prismatic crystals, often acicular, fibrous, or assembled in dark green, olive-green, or grayish radiating aggregates, being an essential component of many crystalline schists resulting from the regional metamorphism of basic magmatic rocks.
• 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.
• Alaite — A rare mineral belonging to the arsenate class, with a complex structural nature, appearing as microscopic crystalline aggregates or efflorescent crusts; a natural chemical compound containing arsenic and hydrated copper, occasionally found in the oxidation zones of polymetallic deposits. This mineral is of particular interest to collectors and geological researchers due to its rarity and specific formation conditions.
• Alochroic — Changing color or displaying different hues depending on lighting conditions, viewing angle, or external thermal factors; a term structurally used to describe minerals or chemical substances whose optical properties induce reversible chromatic variations.
• 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.
• Analcite — An older terminological or spelling variant contextually used for the mineral analcime (analcite), a hydrated sodium and aluminum silicate from the zeolite group. Structurally characterized by white, grey, or colorless isometric (icositetrahedral) crystals, this natural compound forms through hydrothermal processes in the cavities of basaltic magmatic rocks or as an authigenic mineral in some sedimentary rocks, studied in systematic mineralogy for its ion-exchange properties.
• Anatase — A natural mineral form of titanium dioxide (TiO2), crystallizing in the tetragonal system, acting as a low-temperature stable polymorph alongside rutile and brookite. It typically occurs as isolated crystals, often octahedral or bipyramidal, with color variations ranging from yellowish-brown to dark indigo and black, possessing a pronounced adamantine luster. This mineral is extensively studied in materials engineering for its advanced semiconducting properties, utilized in photovoltaic cells and photocatalytic applications.
• Andesine — A mineral belonging to the silicate class, specifically an intermediate variety of plagioclase feldspar, structurally defined by a specific chemical ratio between albite and anorthite (between 30% and 50% anorthite). It is a common constituent of intermediate igneous rocks, such as andesites and diorites, receiving its name from the Andes Mountains, where it was initially identified and abundantly described.
• 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.
• Amphibole — A generic name given to an important group of silicate minerals (inosilicates) rich in iron, magnesium, calcium, and aluminum, crystallizing in monoclinic or orthorhombic systems. These mineral structures are essential components of many igneous and metamorphic rock brands, presenting a characteristic shape of elongated prisms or thin fibers.
• Ankerite — A mineral from the carbonate class, with a crystalline structure similar to that of dolomite, consisting of a calcium, magnesium, iron, and manganese carbonate. This structural mineral is frequently found in metamorphosed sedimentary rocks, in hydrothermal veins, and in association with iron ores, presenting shades from yellowish-white to reddish-brown due to the oxidation of iron exposed to air.
• Antholite — A mineral formation or underground sedimentary concretion, formed through the gradual precipitation and accumulation of mineral salts within specific karst cavities or geological layers. This structural crystalline aggregate often develops in the form of stalactites or branched crusts, having a chemical composition dictated by the cave's microclimate and the purity of hydrothermal solutions circulating through the rock mass.
• Antozonite — A rare variety of radioactive fluorite possessing a dark violet to black color, structurally characterized by microscopic inclusions of free fluorine and colloidal calcium resulting from constant bombardment with alpha radiation from surrounding natural uranium sources. This mineral exhibits the unique property of emitting a pungent odor of fluorine and ozone the moment its crystalline structure is crushed or mechanically fractured.
• Apatite — A mineral from the phosphate class, representing a natural calcium phosphate that contains fluorine, chlorine, or hydroxyl groups within its crystalline structure. This compound is widely used in industry as the primary raw material for producing phosphate fertilizers and phosphoric acid, while also being the most common phosphate mineral in the Earth's crust.
• Azurite — A natural basic copper carbonate mineral with a monoclinic crystal structure, characterized by an intense, glossy, vitreous blue color and a famous chemical instability, often transforming into malachite under the influence of moisture. This structural mineral is found in the oxidation zones of copper ore deposits, historically used as a fine paint pigment and currently as a semi-precious stone for jewelry or decorative objects.