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Aquamarine – one of the birthstones whose name conjures up a color, light greenish-blue, the color of ocean water with the sun on it – hence, aqua marina, Latin for water of the sea. Aquamarine is the traditional birthstone associated with March and the gemstone of the 19th wedding anniversary.
It is one of the beryl group of minerals, that includes emerald (deep green), morganite (pale pink) and heliodor (golden yellow).
- Formula: Be3Al2Si6O18
- Classification: cyclosilicate (6 membered ring)
- Member of the Beryl Group
- Crystal system: hexagonal
- Color: sky-blue to sea-green
- Streak: colorless (harder than streak plate)
- Luster: Vitreous, Sub-Vitreous, Waxy, Greasy
- Diaphaneity: translucent to transparent
- Cleavage: none
- Fracture: conchoidal
- Mohs scale hardness: 7.5 - 8
- Specific gravity: 2.63 – 2.92
The blue coloration is attributed to iron ions within the crystal lattice. The presence of both Fe 2+ and Fe 3+ ions appear to be required for the blue color.
Mineralogy and Geological Occurrence
The color comes from the presence of both Fe 2+ and Fe 3+ in the crystal lattice; quantitites and proportions of the two ions influences the shade of blue-green. Since the deeper blue shades of aquamarine are more valued, many gemstones have been heat-treated to reduce the green shades. The color of heat-treated aquamarines may fade when exposed to sunlight. The habits (external morphology) of aquamarine crystals ranges from acicular (needle-like) to prismatic or tabular habits. Most gem-quality aquamarine crystals formed in cavities in their host pegmatite material, often associated with muscovite and feldspar.
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Aquamarine has been found on every continent except Antarctica. In the United States, gem quality aquamarine has been collected from Colorado, Connecticut, Georgia, Idaho, Maine, New Hampshire, North Carolina, Pennsylvania and Wyoming. Less valuable aquamarine is reported from many other states, including New Mexico.
New Mexico Beryl and Aquamarine
The mineral group beryl has widespread occurrence in New Mexico; it is reported from 11 counties, mostly occurring in pegmatites. Some of these occurrences include the blue variety of beryl, aquamarine. These occurrences are part of the Arizona-New Mexico “beryllium belt”, of note due to the strategic importance of beryllium mining.