Agate

Agate is typically non-toxic unless it's in powder form. Long-term exposure to finely ground powder may lead to silicosis. Therefore, when cutting or polishing agate, be sure to wear a dust mask to avoid inhaling its dust.

Color, pattern, purity, transparency, and weight are the decisive factors affecting the price of agate. At about 2.5 cm in size, the price of an average-quality tumbled stone is usually $.50-$3/piece.

Agate, due to its microcrystalline structure, is known for its exceptional toughness. It can withstand daily wear and tear very well, making it less susceptible to chipping or cracking under normal conditions compared to many other gemstones.

Agate is quite stable in everyday conditions. It manages well against immersions, dryness, and common contaminations. The stone's appearance can withstand household detergents without significant changes, maintaining its visual appeal. Dyed agate may exhibit subtle color shifts.

Lace agate is a variety that exhibits a lace-like pattern with forms such as eyes, swirls, bands or zigzags. Blue lace agate is found in Africa and is especially hard. Crazy lace agate, typically found in Mexico, is often brightly colored with a complex pattern, demonstrating randomized distribution of contour lines and circular droplets, scattered throughout the rock. The stone is typically coloured red and white but is also seen to exhibit yellow and grey combinations as well.

Moss agate, as the name suggests, exhibits a moss-like pattern and is of a greenish colour. The coloration is not created by any vegetative growth, but rather through the mixture of chalcedony and oxidized iron hornblende. Dendritic agate also displays vegetative features, including fern-like patterns formed due to the presence of manganese and iron oxides.

Turritella agate (Elimia tenera) is formed from the shells of fossilized freshwater Turritellas, gastropods with elongated spiral shells. Similarly, coral, petrified wood, porous rocks and other organic remains can also form agate.

Coldwater agates, such as the Lake Michigan cloud agate, did not form under volcanic processes, but instead formed within the limestone and dolomite strata of marine origin. Like volcanic-origin agates, Coldwater agates formed from silica gels that lined pockets and seams within the bedrock. These agates are typically less colorful, with banded lines of grey and white chalcedony.

Greek agate is a name given to pale white to tan colored agate found in Sicily, once a Greek colony, back to 400 BC. The Greeks used it for making jewelry and beads.

Brazilian agate is found as sizable geodes of layered nodules. These occur in brownish tones inter-layered with white and gray. Quartz forms within these nodules, creating a striking specimen when cut opposite the layered growth axis. It is often dyed in various colors for ornamental purposes.

Polyhedroid agate forms in a flat-sided shape similar to a polyhedron. When sliced, it often shows a characteristic layering of concentric polygons. It has been suggested that growth is not crystallographically controlled but is due to the filling-in of spaces between pre-existing crystals which have since dissolved.

Other forms of agate include Holley blue agate (also spelled "Holly blue agate"), a rare dark blue ribbon agate only found near Holley, Oregon; Lake Superior agate; Carnelian agate (has reddish hues); Botswana agate; plume agate; condor agate; tube agate containing visible flow channels or pinhole-sized "tubes"; fortification agate with contrasting concentric banding reminiscent of defensive ditches and walls around ancient forts; Binghamite, a variety found only on the Cuyuna iron range (near Crosby) in Crow Wing County, Minnesota; fire agate showing an iridescent, internal flash or "fire", the result of a layer of clear agate over a layer of hydrothermally deposited hematite; Patuxent River stone, a red and yellow form of agate only found in Maryland; enhydro agate contains tiny inclusions of water, sometimes with air bubbles.

Agate minerals have the tendency to form on or within pre-existing rocks, creating difficulties in accurately determining their time of formation. Their host rocks have been dated to have formed as early as the Archean Eon. Agates are most commonly found as nodules within the cavities of volcanic rocks. These cavities are formed from the gases trapped within the liquid volcanic material forming vesicles. Cavities are then filled in with silica-rich fluids from the volcanic material, layers are deposited on the walls of the cavity slowly working their way inwards. The first layer deposited on the cavity walls is commonly known as the priming layer. Variations in the character of the solution or in the conditions of deposition may cause a corresponding variation in the successive layers. These variations in layers result in bands of chalcedony, often alternating with layers of crystalline quartz forming banded agate. Hollow agates can also form due to the deposition of liquid-rich silica not penetrating deep enough to fill the cavity completely. Agate will form crystals within the reduced cavity, the apex of each crystal may point towards the center of the cavity.

The priming layer is often dark green, but can be modified by iron oxide resulting in a rust like appearance. Agate is a very durable and therefore is often seen detached from its eroding matrix, once removed, the outer surface is usually pitted and rough from filling the cavity of its former matrix. Agates have also been found in sedimentary rocks, normally in limestone or dolomite; these sedimentary rocks acquire cavities often from decomposed branches or other buried organic material. If silica-rich fluids are able to penetrate into these cavities agates can be formed.

Agate is one of the oldest stones to be molded by people, and has been used for tools and as a gemstone for thousands of years. Today, its ornamental uses include making cabochons and beads for jewelry, small sculptures, functional objects such as paperweights, and rarely marbles. Agate is also a popular tumbled stone. It is porous and can be easily dyed.

Used since ancient times in many cultures, agate has been extremely valued. This gemstone has numerous varieties and each one of them was associated with different beliefs, although generally agate has been used as a protection against evil. It was also used to ward off fears, insecurities, envy, and jealousy.

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 or Achates (Ancient Greek: Ἀχάτης) in Sicily, sometime between the 4th and 3rd centuries BC.

Agate is considered a grounding stone that has many different healing effects depending on the color of the stone. When used during meditation it may enhance spiritual awareness and stimulate psychic abilities. Along with that awareness comes self-truth and a building of self-esteem and confidence.