Colombianite

Colombianites are natural volcanic glasses from western Colombia. The material is also known as Cali glass and may resemble tektites in appearance. However, modern scientific analyses have confirmed that it is rhyolitic volcanic glass – obsidian, not glass formed by the impact of a cosmic body.

They are characterized by a dark gray to almost black color and a strongly pitted, sculpted surface. Under strong transmitted light, many specimens display smoky brown, gray-brown to olive shades. Individual specimens vary in shape, translucency and the intensity of their surface sculpture.

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How Did Colombianites Form?

Colombianites formed during volcanic activity in the Pliocene. Silica-rich rhyolitic melt cooled and solidified into natural volcanic glass. Dating of Cali glass samples has determined their age at approximately 3.25 million years.

Their chemical composition, the presence of layers and small mineral particles, isotopic composition and water content are consistent with volcanic glass. These properties have also made it possible to rule out the previously discussed possibility that colombianites are tektites or another type of impact glass.

Why Do Colombianites Resemble Tektites?

Primarily because of their irregular shapes and deeply pitted surfaces, colombianites can resemble some tektites at first glance. This similarity was one of the reasons their origin was debated in the past, and colombianites have also been referred to as pseudotektites.

Their present-day surface appearance, however, developed mainly through long-term dissolution, weathering, erosion and fluvial processes in a tropical environment. These processes gradually created the characteristic pits, grooves and other surface structures.

Colombianites from Valle del Cauca

The specimens in this selection come from the Valle del Cauca region of Colombia. Natural glasses occur here in the river valley and in associated weathering deposits and sediments. Individual pieces may have rounded, oval or irregular shapes, and each specimen has its own unique surface structure.

Appearance in Transmitted Light

Although colombianites often appear almost black and opaque under normal lighting, they may become distinctly translucent when illuminated with a strong light source. They most commonly display smoky brown, gray-brown to olive shades, which are among their most distinctive visual characteristics.