Volcanic rocks prevalent at Crater of Diamonds

The Crater is home to many other rocks and minerals, including jasper, sandstone, conglomerate, agate, quartz, amethyst, calcite, barite, mica, and (of course) diamonds, but the most prominent elements of the Crater are its volcanic rocks.

The park's 37.5-acre diamond search area is composed of three types of volcanic rocks-black lamproite, green volcanic tuff, and white volcanic lapilli. According to geologists the Prairie Creek Diatreme, the volcano which formed the Crater of Diamonds, originally erupted when much of southern Arkansas was under an ancient, shallow sea. Lamproite lava pushed the diamond-bearing volcanic tuff from deep underground. At the surface, heat from the lava turned groundwater into steam. Volcanic ash particles stuck together with water droplets in the air and fell back into the crater as lapilli.

The volcanic rocks found in the search area are made of many minerals. Lamproite often contains olivine and manganese. Olivine appears as tiny green or yellow speckles, and manganese creates a dark purple color. Some lamproite contains white bands of hydroxylapatite, a clay-like mineral which is also found in our bones. Volcanic tuff may have glittery mica along its surface, making it appear especially beautiful in sunlight.

If you are unable to find a diamond during your visit, these stones make excellent mementos of your trip into a diamond-bearing volcanic crater. These intriguing elements can be tumble polished for display, but a quick way to beautify them is with a coat or two of spray polyurethane.

To preserve delicate minerals in the rocks like calcite, lightly brush or rub away dirt and hit the stone with a light spritzing of polyurethane clear coat. Polyurethane for outdoor use generally leaves a thicker layer of clear coat on the stones. Once the initial coat has dried, the spray can be reapplied as often as needed to maintain a gloss-like finish.

The finished stones can be displayed indoors to maintain their appearance longer, and they will make excellent conversation pieces from your visit to the Crater of Diamonds.

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