Crystal Geode, Amethyst, 10"-15", Purple Crystal

Introduction
Geode, also known as crystal ball, is a common geological formation in the United States, Brazil and Mexico. It is essentially composed of bubble crystals inside the rock. Generally, the interior contains quartz crystals and chalcedony deposits, and its exterior is limestone. or related rocks. Others that are completely filled with crystals are called nodules.

Composition characteristics
The variety of crystal sizes, shapes and shades of color makes each geode unique. Some are pure quartz crystals, others are deep purple amethysts. Others may be agate, chalcedony or jasper, etc. Only cutting or breaking a geode can determine if it is solid and what crystals it contains.

Cause of formation
Geologists do not yet have a widely accepted theory of geode formation, but believe that geodes can form in any buried cavity. These cavities can be air bubbles in igneous rock, cavities under tree roots, or even burrows dug by animals. Over time, the outer walls of the cavity hardened and dissolved silicates and calcite were deposited on the inner walls. Over a long period of time, the slowly infiltrating minerals caused the crystals to crystallize inside the cavity. Then, over millions of years, the geodes were moved back to the geological surface.

Example
The "Great Crystal Cave" is located in a mining cave in the southern Chihuahua region of Mexico. These crystals form in a natural cave surrounded by bedrock. Some of the spectacular crystals in the geodes are as tall as pine trees, and others are very large in circumference, and they are all translucent gold or silver in incredible shapes and structures. At the same time, some limestone bodies were also found in the large crystal cave. This kind of limestone often appears in ores such as silver, zinc or lead during mining. It is likely that gypsum crystals appeared in the decomposition of hydrothermal deposits during the process of mineral shrinkage and decline. formed during transformation.
Submerged in mineral-rich water, crystals grow quickly. The temperature of these waters is stable, usually around 58 degrees Celsius. At this temperature, anhydrite combines with water to form gypsum, which accumulates over time to form crystals in caves.