Agate, Botswana

Mineralogy of Botswana Agate

Rough Botswana Agate, Botswana

Mineral Family: Tectosilicates

Chemical Composition: SiO₂ 
Cleavage: None
Color: Pink and grey banded
Crystal System: Trigonal
Form/Habit: Tectosilicate
Fracture: None
Gravity: 2.6-2.64
Hardness: 6.5-7
Luminescence: Green (long wave) / Yellowish-white (short wave)
Luster: Vitreous
Streak: White
Transparency: Opaque

Location: Agates are found all over the world, however this particular form of Agate is found exclusively in Botswana.

Mineral Family: Botswana Agate is a rare type of Silicate mineral. Silicate minerals form the largest family of minerals, including more than 25% of all known minerals and 40% of all common minerals. In addition to being a major part of the Earth’s crust, Silicate minerals have also been found on the moon and in meteorites. Silicates are minerals which contain the elements Silicon (a light gray shiny metal) and Oxygen (a colorless gas). Together, these two elements form a tetrahedron – a shape similar to a pyramid – with a Silicon atom in the center and Oxygen atoms at each of the four corners. These tetrahedra connect with other chemical structures, in six different ways, to form various minerals and rocks. There are six main groups of Silicate minerals, and these main groups are further subdivided into secondary subdivisions, such as Quartz and Feldspar. Quartz is a large mineral family in its own right, and has two main subdivisions, macrocrystalline (crystals that are large enough to be seen by the naked eye, for example, Amethyst) and microcrystalline (crystals so small they can only be seen through a microscope, for example Carnelian). All microcrystalline Quartz fall under the subcategory of Chalcedony, which is then further subdivided. One of these categories is Agate. Botswana Agate is found only in the southern African country from which it takes its name, and is famous for its natural pink and orange hues in addition to soft grey, blue and purple rings.

Formation: Botswana Agate is created when liquid magma flowing in long fault lines cools down and transforms into igneous rocks. During this cooling down period, thin streams of silica acid shift from being a gas/liquid into a solid compound. These thin layers of silica acid stack on top of one another, creating extra fine banding and patterns in a variety of colors.

Mining: Agates are typically mined from primary deposits that still have their original relationship with the host rock. Agates are usually ball or almond-shaped nodules ranging in size from a fraction of an inch to several yards in diameter. If the Agate fills the entire hollow space left by the gas bubble, it is called an Agate Almond. If a hollow remains in the center, it is called an Agate Geode.  In the case of Botswana Agate, Agate Almonds are often found in secondary alluvial deposits, notably along the Bobonong River.

Agate Depost on the Bobonong River, Botswana

Enhancements: Agates are porous and have been dyed bright colors since the Roman Era.  As a general rule, the more vivid the coloring, the more likely that it has been dyed. This is particularly true if the color is vivid while the price is cheap! With most Agates there will be “hard” spots that are bright white which won’t take dye, while other areas are “soft” and take dye easily.  Currently most of the dyed Agates come from Brazil.  They are naturally a pale grey and white stone, but are dyed vivid colors like hot pink, deep purple or bright blue.  By contrast, Botswana Agates are fully natural and have been enhanced only by cutting, tumbling, and polishing. 

Synonyms: Sunset Stone

Map courtesy of TravelBlog
Photos: Botswana Agate, Bobonong River, Dyed Agates