Aquamarine is a highly sought-after gemstone recognized for its striking blue to cyan coloration, often evoking the clear color of seawater. This popular stone is widely appreciated in jewelry for its notable transparency and resistance to wear. The name originates from the Latin words aqua (water) and marina (sea), an appropriate descriptor for its characteristic hue.
The Beryl Mineral Family
Aquamarine is a color variety of the mineral species known as beryl. Beryl is chemically defined as a beryllium aluminum cyclosilicate (Be3Al2Si6O18). The presence of beryllium is a defining characteristic of the beryl group, contributing to the stone’s brilliance.
Pure beryl, which lacks color-causing impurities, is known as colorless goshenite. Aquamarine shares this fundamental crystal architecture with other famous gemstones differentiated by trace elements. These members include intense green emerald (colored by chromium or vanadium) and pink-to-peach morganite (colored by manganese).
The Chemical Basis of Aquamarine’s Color
The distinctive blue hue of aquamarine is caused by trace amounts of iron within the crystal structure. The light blue color is attributed to ferrous iron (Fe2+) ions replacing aluminum atoms in the beryl’s lattice. When ferric iron (Fe3+) is also present, it introduces a yellowish component that results in the greenish-blue coloration often found in natural specimens.
The gem industry routinely uses heat treatment to remove this greenish tinge and achieve a purer, more saturated blue. Heating the stone, typically between 400°C and 450°C, alters the oxidation state of the iron impurities. This process converts the yellowish Fe3+ ions into the blue-producing Fe2+ ions, making the resulting blue color permanent and more pronounced.
Identifying Physical Characteristics
Aquamarine is considered a durable gemstone due to its high ranking of 7.5 to 8 on the Mohs scale of mineral hardness. This means it is significantly resistant to scratching from most common materials. The stone typically forms long, prismatic crystals with a characteristic six-sided cross-section. Aquamarine is highly prized for its exceptional transparency, often noted as a Type I clarity stone, and possesses poor or indistinct cleavage.
Geological Origins and Major Sources
Aquamarine crystals form deep within the Earth under conditions of high temperature and pressure. The mineral is primarily found within granitic pegmatites, which are coarse-grained igneous rocks that crystallize from a magma body’s residual melt. The slow cooling of these pockets provides the necessary time and space for the aquamarine to develop into large, well-formed crystals.
Aquamarine can also be recovered from alluvial deposits, where weathering has washed the harder crystals into stream sediments. For over a century, Brazil has been the world’s leading source for high-quality specimens, particularly from the state of Minas Gerais. Other significant global sources include Pakistan, Nigeria, Madagascar, and Mozambique.