Aquamarine is a variety of the mineral beryl, which is a beryllium aluminum silicate. This gemstone is chemically identical to emerald and other beryl varieties, differing only in the trace elements that give it color. The name itself is derived from the Latin phrase aqua marina, literally meaning “water of the sea,” a direct reference to its characteristic hue.
Primary Visual Characteristics
Raw aquamarine typically displays a color palette ranging from a very pale blue to a more pronounced greenish-blue or sea-green. This coloration comes from iron impurities within the beryl crystal structure, specifically the presence of ferrous iron (\(\text{Fe}^{2+}\)). Unlike finished gemstones, the raw material often retains a noticeable green tint, sometimes appearing murky or grayish-blue depending on the iron concentration.
The clarity of raw aquamarine is highly variable, often appearing translucent or opaque rather than perfectly transparent. Many natural specimens contain internal features such as fractures, liquid-filled tubes, or needle-like inclusions known as “rain inclusions” or “silk.” A clean, exposed face of the crystal will exhibit a vitreous or glassy luster, though the surfaces of a naturally extracted piece may be duller, covered in earthy residue, or etched by the surrounding environment.
Typical Crystal Habit
Aquamarine is part of the hexagonal crystal system, meaning its structure is based on a six-sided symmetry. The raw crystals characteristically form as prismatic columns, resulting in a six-sided shape when viewed in cross-section. These crystals are typically elongated, with some natural specimens growing to be quite massive in size, though most collectible raw pieces are smaller.
The long faces of these hexagonal prisms often display fine, parallel lines or grooves, known as vertical striations, running along the length of the crystal. The ends of the crystal, known as the terminations, can be flat (pinacoidal) or feature complex, pyramid-like faces. However, it is very common for raw crystals to be found with broken or incomplete terminations, as the extraction process often separates the crystal from the host rock at a point of weakness.
Geological Setting and Matrix
The term “raw” aquamarine often means the specimen is still within or attached to its surrounding host rock, referred to as the matrix. Aquamarine forms primarily in granite pegmatites, which are extremely coarse-grained igneous rocks that cool slowly underground. These pegmatites are the last portion of a magma body to crystallize, creating a fluid-rich environment that allows for the growth of large crystals.
The surrounding matrix frequently includes other minerals common to pegmatite deposits, such as white or tan feldspar, quartz, and various types of mica like muscovite. The surface of the raw crystal may also show rough, uneven areas where it was forcibly broken away from the matrix during mining.