A dendrite is a natural tree-like or moss-like formation on, or in, a piece of rock or mineral. A dendritic pattern forms when an element or mineral, starting from a point of origin, migrates and branches outward. A single dendritic branch extends until the mineral reaches a point where growing various new branches is, for some unknown reason, more favourable.
Dendritic crystallization forms a natural fractal pattern. Dendritic crystals can grow into a supercooled pure liquid or form from growth instabilities that occur when the growth rate is limited by the rate of diffusion of solute atoms to the interface.
|Dendritic Agate from India
The surfaces of limestones are often marked by black or red-brown deposits known as mineral dendrites. These are deposits of hydrous iron or manganese oxides formed when supersaturated solutions of iron or manganese penetrate the limestone and are precipitated on exposure to air at the surface. Mineral dendrites have a fractal appearance, but the origin and characteristics of this morphology,The term "dendrite" comes from the Greek word dendron, which means "tree".
Examples of dendrite minerals include
- Manganese oxides: These black or brown minerals are often seen on the surfaces of rocks like limestone and sandstone. They form when manganese-rich groundwater comes into contact with air.
- Iron oxides: These red or brown minerals are also common on rock surfaces. They form in a similar way to manganese oxides, but from iron-rich groundwater.
- Native metals: Some metals, like gold and silver, can also form dendritic crystals. These are less common than dendritic minerals, but they can be very beautiful.
- Copper: Copper dendrites are typically green or blue and can be found on rocks such as malachite and azurite.
|Manganese dendrites on a limestone bedding plane from Solnhofen, Germany.
In paleontology, dendritic mineral crystal forms are often mistaken for fossils. These pseudofossils form as naturally occurring fissures in the rock are filled by percolating mineral solutions. They form when water rich in manganese and iron flows along fractures and bedding planes between layers of limestone and other rock types, depositing dendritic crystals as the solution flows through
|Dendritic Quartz From Brazil.
How Dendrite Minerals form
There are two main ways that dendrite minerals can form:
Crystallization: When a mineral solution cools rapidly, it can become supersaturated, meaning that it contains more dissolved mineral than it can normally hold. This can cause the mineral to crystallize out of the solution in a rapid and uncontrolled manner, leading to the formation of dendritic crystals.
Precipitation: When a mineral-rich solution comes into contact with another solution that causes the mineral to precipitate out, the mineral can form dendritic patterns if the precipitation process is slow and uneven.