Exquisite Tall Arrowhead-Shaped Blue Lace Agate Geode Slice on Wooden Stand. This specimen would make an incredible addition to any mineral collection, and serve as a conversation piece or focal point to a display shelf. 

Size: 13 x 2 x 18 in. 

Agate is the banded variety of chalcedony which comes in a wide variety of colors. Primarily formed within volcanic and metamorphic rocks, the ornamental use of agate was common in Ancient Greece in assorted jewelry and the seal stones of Greek warriors, while bead necklaces with pierced and polished agate date back to the 3rd Millennium BC in the Indus Valley civilization. The stone was given its name by Theophrastus, a Greek philosopher and naturalist, who discovered the stone along the shore line of the Dirillo River in Sicily in the 4th Century BC. Agate minerals have the tendency to form on or within pre-existing rocks, creating difficulties in accurately determining their time of formation. It is one of the most common materials used in the art of hardstone carving, and modern industrial uses of agate exploit its hardness, ability to retain a highly polished surface finish, and resistance to chemical attack. It has traditionally been used to make knife-edge bearings for laboratory balances and precision pendulums, and sometimes to make mortars and pestles to crush and mix chemicals.

A geode is a geological formation within sedimentary and volcanic rocks. They are hollow, vaguely spherical rocks, in which masses of mineral matter which may include crystals are secluded. The crystals are formed by the filling of vesicles in volcanic and subvolcanic rocks by minerals deposited from hydrothermal fluids. After rock around the cavity hardens, dissolved silicates and/or carbonates are deposited on the inside surface. Bedrock containing geodes eventually weathers and decomposes, leaving them present at the surface if they are composed of resistant material such as quartz. When cut in half, visible bands corresponding to varied stages of precipitation may at times show patterns that reveal points of fluid entry into the cavity and/or varied colors corresponding to changes in chemistry. Geodes are found where the geology is suitable with many of the commercially available ones coming from Brazil, Uruguay, Namibia, and Mexico. Geodes are also common in some formations in the United States (mainly in the Midwest and some parts of the Southwest) as well as parts of England and northern Asia. While the term “geode” generally describes hollow formations, if the rock is completely solid inside (often filled with chalcedony) it would be classified as a “nodule” or “thunderegg.”