5.1" Las Choyas "Coconut" Geode Half with Amethyst & Calcite - Mexico

This is a beautiful "coconut geode" half from Chihuahua, Mexico. It's lined with a mixture of sparkling amethyst and calcite crystals. The brown inclusions within the amethyst are fibrous goethite formations which are especially gorgeous under magnification. Comes with an acrylic display stand.

Geodes are rounded, hollow voids in rocks filled with crystals and other minerals. They are typically formed when air bubbles inside of volcanic rock form hollow cavities. Over time, as mineral-rich water seeps into the rock it beings to deposit tiny crystals on the sides the hollow cavity. After millions of years, the flow of water gradually builds crystals inside the empty space.

Las Choyas geodes, often referred to as coconut geodes are mined from 100 to 200 feet below the surface near Chihuahua, Mexico. Shafts are drilled down to the geode bearing white clay, and then tunnels are dug horizontally to extract the geodes.

The geodes typically range from about 2-6 inches in diameter and can contain a variety of minerals and crystals. Most hollow geodes contain a variety of quartz ranging from clear quartz to smoky quartz to more rarely amethyst. Many secondary minerals such a goethite, hematite, mordenite, calcite and galena may also be present in some geodes.

Amethyst is a purple variety of quartz (SiO2) and owes its violet color to natural irradiation, iron impurities, and the presence of trace elements, which result in complex crystal lattice substitutions. It’s considered a semi-precious gemstone, and just two centuries ago was considered to have a value on par with diamonds, sapphires and rubies. The largest and best known amethyst deposits occur in southern Brazil and Uruguay but many localities around the world produce an amazing variety of amethyst crystals and formations.

Silicon Dioxide, also known as SiO2 or Quartz, is the second most abundant mineral in the Earth's crust. Quartz crystals generally grow in silica-rich, hot watery solutions called hydrothermal environments, at temperatures between 100°C and 450°C, and usually under very high pressure. Quartz veins are formed when open fissures are filled with hot water during the closing stages of mountains forming, and can be hundreds of millions of years old.

Calcite, CaCO3, is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs are the minerals aragonite and vaterite. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, and prisms. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form.

Known since ancient times, Goethite is a beautiful dark gray to black iron-based mineral that can take many forms. It was used in antiquity as a pigment for painting and has even been found in the famous caves at Lascaux, France.
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DETAILS
SPECIES
Quartz var. Amethyst, Goethite & Calcite
LOCATION
Chihuahua, Mexico
SIZE
5.1" wide
CATEGORY
SUB CATEGORY
ITEM
#145870