How do agates form

Cryptocrystalline means that the mineral crystals are so fine that they are only vaguely seen in patterns and fine variations.

Name: The name is derived from its occurrence at the Achates River in southwestern Sicily. A distinctly banded fibrous chalcedony. Most agates occur as nodules in volcanic rocks or ancient lavas, in former cavities produced by volatiles in the original molten mass, which were then filled, wholly or partially, by siliceous matter deposited in regular layers upon the walls.

Agate has also been known to fill veins or cracks in volcanic or altered rock underlain by granitic intrusive masses. Such agates, when cut transversely, exhibit a succession of parallel lines, often of extreme tenuity, giving a banded appearance to the section.

Agates contain quartz but the quartz inside agates is not just ordinary quartz. Agates contain both chalcedony and pure quartz. TIP: You already know everything about agates. I think it is time to find some coll agate now. But do you know where? Feel free to read it here:. Rock Hammer vs. Brick Hammer: Explained Usage for Rockhounding.

Table of Content. What is agate? How does the agate form? What are the main types of agates? Are all the colors in an agate real? What does agate look like in nature? How can you tell if a rock is an agate? FAQ about Agate Rocks. There are numerous methods of dying agates , some of which include: Boiling the stone in a solution containing dye the heat expands the stone making it easier for the dye to enter , Heating up the stone in a solution containing dye then dropping it into a cold solution the rapid temperature drop causes fractures which make it easier for the dye to penetrate different parts of the stone , Boiling the stone in a bicarbonate solution than putting the stone in a different chemical solution the chemical used depends on what color you want the rock to be.

Accumulation of the dye — if you look closely and see areas that have darker coloring, this could be a sign that the dye accumulated in that area, making that part darker than the rest of the agate. Areas like these are usually fractures and pits. If you break a dyed agate, the color inside will definitely be different from the color it has on the outside. Features swirls, twisted bands, and circular patterns in a variety of colors, especially red, gold, brown, white, and cream. Also translucent with black or brownish inclusions in the shapes of trees or ferns.

Those that look like real landscapes are very valuable and collectors are always on the lookout for them. An expensive type of agate that displays iridescence play of colors when viewed from different angles. The iridescence is the result of limonite or goethite inclusions.

They nucleate on the wall and radiate inward like spokes on a bicycle wheel. Usually the first layer is a very fine-grained material, chalcedony, which is a mixture of quartz and moganite. Then you have coarse-grained quartz layers—pure quartz, no moganite. They're both silicon dioxide. What is changing is the crystal structure.

They grow in a helical fashion. The chalcedony fibers grow perpendicular to the normal growth direction. These repeating changes in crystal size, type, and direction, Heaney believes, causes the characteristic banding pattern of the agate, the colors coming from trace elements like iron or manganese. It's like a Russian doll. There's hierarchical layering. I'm not aware of any completely non-biological mechanism that accounts for this kind of layering in natural materials.

How do you explain it? If there is water nearby, there is a chance that silica-rich water will fill up one or more of these empty vesicles. If the silica is concentrated enough or some of the water evaporates , it acquires a gel-like consistency. What follows is a slow process of solidifying as the silica molecules rearrange and begin forming fibrous micro-crystals along the sides of the cavity.

The bands of color you see are usually the result of other impurities which the water carried in. Sometimes the entire vesicle fills in with solid agate rock, while other times the silica is used up before the rock can be filled completely. This is when you get a hollow rock known as a geode. Geodes are not always formed out of volcanic rock, and may not always be made of agate.

Sometimes they form in sedimentary rocks instead, forming through different but similar processes which produce the geode effect. Chalcedony is still the most common component, though other types of crystals may also be present, including pyrite, calcite, and barite.