New! Aquamarines from Guaratinga (Jaquetô), Bahia, Brazil
Crystal Classics and Kristalle's recent website update features a selection of beautiful and mineralogically interesting Aquamarine crystals from Guaratinga (Jaquetô), Bahia, Brazil.
Jaquetô is a known locality for Aquamarine crystals which show interesting and unique crystallisation, forms, and etching. These specimens all came from an old find, and were only recently acquired by ourselves as one batch. Another known find of etched Aquas at Jaquetô occured around Sept 1990, these were of a medium blue colour.
Aquamarine is a variety of Beryl (Be3Al2Si6O18), which is classed as a Cyclosilicate, part of the Silicates group, which also includes the common rock forming minerals. Beryls, however, are far from just a common mineral, they are prized for their beautiful colours, both as aesthetic mineral specimens and also as cut gems. There are several varieties of Beryl, which are based on colour:
- Aquamarines (pale to medium blue, and bluish-green/greenish-blue)
- Emeralds (pale to dark green)
- Morganite (pinks)
- Goshenite (colourless)
- Helidor (gem quality golden Beryl).
It commonly forms a hexagonal prismatic crystal with flat or tapered terminations.
Beryls are commonly found in Pegmatites, and when found on matrix (which is not that common an occurence) are often associated with pegmatite minerals - such as Feldspars, Micas. They may also form in metamorphic schists, such as the Emeralds in Biotite schists from the Ural Mountains, Russia.
The Aquamarines from Guaratinga are all a beautiful pale sea-green colour. Most are undamaged, and many do not show any contact to matrix, suggesting they may be floaters. They have a range of forms, and not all are regularly formed, each creating its own unique specimen. All of the Aquas are very gemmy, many completely internally flawless, and only a very few with inclusions. All most all of the Aquas are undamaged.
The specimens have a range of shapes. Some are very thin and elongate, with well defined hexagonal shape to a more rounded cylindrical shape, and tapered double terminations. They resemble torpedos, or even a sharpened pencil where the hexagonal crystal shape is sharply defined.
Other specimens are short in comparison, barrel shaped with curved sides and no distinct crystal faces, and flat end terminations. Others are a mix of the two, barrel shaped with slightly tapered terminations ending in a flat c-faces.
What makes these specimens so interesting and unusual, apart from the crystal shapes, is their etching. Each one is entirely unique, created by minute variations in the environmental conditions.
Minerals generally form from solutions, with the elements crystallising out, and the best crystals form within a narrow range of environmental conditions. Often a change in conditions may mean the crystal will begin to dissolve rather than grow. This dissolution can occur as 'etching' where distinct pits may form in a smooth crystal face. Etch marks are related to the crystal structure, and certain pit shapes will only form on certain crystal faces. In Beryls, on the end terminations (c-face) pits may be hexagonal shape the same as the crystal shape. On the crystal faces on the length of the crystal, the etched pits will commonly be elongate and aligned parallel to the direction of the c-axis.
Etch pits resembling capital 'I's aligned parallel to the c-axis
The etch pits are all well defined, but vary in size and placement
The flat termination of a crystal shows hexagonal shaped etch pits, as determined by the Beryl crystal structure.
We believe the Aquamarine crystals had been originally well formed when the environmental conditions changed and they came in contact with solutions depleted of Aquamarine forming elements. They began to etch, with distinct regular pits forming on the crystal faces along the length of the crystal. The pits are parallel and elongate in the direction of the c-axis. They somewhat resemble capital 'I's, and vary in size and length. Some specimens show elongate slits or channels, usually parallel to the c-axis, which may be a very long etch pit, or where there was included material in the Aqua. A few specimens also have etch pits on their terminations and these are hexagonal in shape.
Guaratinga (Jaquetô), Bahia, Brazil is located on the eastern central side of Brazil, just north of Minas Gerais. The area has gem bearing pegmatites where the Aquamarine crystals are found.
We hope you find these Aquamarine crystals as beautiful and fascinating as we have!
