1.65" Keokuk "Red Rind" Geode with Pyrite - Iowa

This is a beautiful, sparkling quartz "red rind" geode from the Keokuk area of Iowa. It's been cracked open to reveal an interior lined with glimmering, clear quartz crystals and pyrite. Both halves are included.

These specific geodes are called "red rind" geodes due to the reddish coloration of their sides. They come from only a couple of specific sites in the Keokuk area and are know for their water clear quartz crystals.

Unlike most geodes that form in volcanic rock, Keokuk geodes are found in the sedimentary rock. They started out as concretions, balls of mud, which formed around organic material about 340 million years ago. The outer shells of these concretions were subsequently replaced by chalcedony and the interiors of the concretions were dissolved, leaving a hollow space into which quartz crystals could grow. Most geodes are 2 to 5 inches wide, though specimens as large as two feet across have been found.

Keokuk geodes contain a variety of minerals, but quartz is dominant in most. Many geodes are filled with clear to white quartz crystals. Micro-crystalline quartz, or chalcedony, whose component crystals are too small to be seen with the naked eye, forms the outer shell. Chalcedony layers also encrust the interior walls of many geode cavities, covering the surfaces of the earlier-generation quartz crystals in a variety of colors, including white, gray, blue, yellow and orange. Calcite is also a common mineral in many geodes though 17 other minerals have been identified in Keokuk Geodes including pyrite and sphalerite.

The area around Keokuk, Iowa is sometimes referred to as “the geode capital of the world. In 1967 they were even named the official state rock of Iowa. Geodes have been collected from the Lower Warsaw Formation within about 100 miles of the city for over 150 years.

Silicon Dioxide, also know 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.

The mineral pyrite or iron pyrite is commonly referred to as Fool's Gold because its metallic luster and pale brass-yellow hue give it a superficial resemblance to gold. In the old mining days, pyrite was sometimes mistaken for gold. Pyrite is the most common of the sulfide minerals with the chemical formula FeS2. Pyrite crystals occur in many shapes and habits, including cubes of all sizes, penetration twin cubes, pyritohedral clusters and as small druzy crystals that can exhibit a beautiful glistening effect.
DETAILS
SPECIES
Quartz & Pyrite
LOCATION
Keokuk area, Iowa
SIZE
1.65" wide (each half)
CATEGORY
SUB CATEGORY
ITEM
#141506