Mainly made up of the Guiana Shield, a very large geological feature that covers Guyana and Suriname. Stones like granite, quartz diorite, and other volcanic rocks like basalt and andesite are common in Suriname.
Suriname is said to have an ever changing coastline due to erosion of the stones that make up the coastline.
The most notable geological feature in French Guiana is the guiana shield. Studies of the shield are often focused on magnetism measured in the rock to map the large formation.
Types of Rocks in French Guiana
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Granite is plentiful in French Guiana and it extends across the country and forms the basement of the rain forest in French Guiana.
Granite is a colorful coarse grained volcanic rock. It is an intrusive rock that cools slowly deep in the earth before it is pushed to the surface through tectonic or volcanic action.
Granite ranges in color from white to balck, with greens, yellows, browns and pinks also common.
Granite is used decoratively and for construction and is quarried around the world and exported.
In French Guiana, however, the granite forms plateaus called inselbergs that support unique ecosystems with delicate flora and fauna. Conservation efforts in French Guiana focus on these special places.
The granite is mostly found in central French Guiana.
Quartz diorite is a common construction material in roads and paving. It is a coarse grained intrusive volcanic rock that forms deep in the earth as molten rock cools slowly resulting in the coarse grained appearance.
The stone is often cut for paving and gravel to mitigate erosion.
Quartz diorite in French Guiana makes up a large portion of the guiana shield in central French Guiana. The stone can be found in and around the rainforests that stretch from Venezuela into French Guiana.
These stones are not young in French Guiana, they are estimated to be billions of years old.
Haematite, sometimes spelled hematite, is an iron rich crystal that can be found in volcanic stones and soil.
Haematite is black, gray, brown or reddish brown due to the level of oxidation of the iron in the crystals. It is chemically identical to rust.
Hematite is mined for iron ore.
Red hematite is the substance that was ground and used for some of the earliest human art and cave paintings.
It is believed to be a grounding stone and is used in healing jewelry and religious practices.
The iron content has a very small magnetic, but measurable magnetic moment. This is one of the minerals that is used to study the size and shape of the guiana shield.
Hematite crystals have been found when mining in the guiana shield in French Guiana.
Similar to hematite, magnetite is an iron ore made up of iron I and iron II. It is sometimes called magnetic iron ore.
It is black to gray but can be red or reddish brown due to the level of oxidation of the iron. It has an iridescent luster.
It is a crystal structure that is hexoctahedral and looks like small pyramids in many cases.
It has been found in Tamanoir in French Guiana. It is important to remember that samples that have been found in French Guiana may be listed as being found in France as it is completely incorporated with France.
The defining characteristic of magenitie is its strong magnetism. This is measured in the guiana shield and used to measure the size and shape of the formation.
It is also believed that the magnetic properties of the stone play a role in migration of salmon and migration of other animals.
Kimberlite & Lamperlite
Kimberlite and lamproite are intrusive volcanic rocks that form deep in the earth and are pushed slowly to the surface.
These two rocks are known to often deliver diamonds to the surface where they can be mined and polished.
Kimberlite is primarily olivine and is found in the guiana shield in the center of French Guiana.
It forms in vertical pipe-like formations and is often mined in open pit mines. They are the target of diamond hunters.
It is relatively rare, but has a very obvious conglomerate appearance with bright embedded crystals and micas.
Lamperolite is another olivene containing intrusive volcanic rock. It also contains large and small crystals of mica, olivene, and other minerals.
Lamperlite was once called kimberlite II, because they appeared to be so similar, but closer inspection shows that lamproite and kimberlite are entirely distinct.
The guiana shield is an uncommonly old formation. The rocks that are contained in the formation are estimated to be more than a billion years old.
Komatiite is one of the very old rocks found in French Guiana. It has a reddish brown, gray to green.
The rock is rare and is believed to be formed at very high temperatures. It contains high levels of olivine and magnesium.
Komatiite contains diamonds, but the formations are quite unlike kimberlite and lamproite.
Greenstones (Basalt and Andesite)
Greenstone belts are areas where the stone appears green to the eye and contain large amounts of olivine.
Here the volcanic rocks basalt and andesite have come from deep in the earth and cooled quickly after they were extruded to the surface.
These rocks are common volcanic rocks and can be found closer to the coast in French Guiana.
Rocks in French Guiana
French Guiana is known for the ever changing coastline due to the movement of minerals and mud by rivers to the coastline.
The geology in French Guiana is unique and powerful. The changing coastline, the ancient stones, the rainforest inselbergs and the diamonds make it an exciting destination for rock lovers.
Conservation efforts in French Guiana focus on preserving the biodiversity in the rain forests, but collection or removal of rocks and stones is also prohibited in protected areas.
Be sure to obey any posted signs and local laws when collecting and removing any stones, sand or shells.
Consider purchasing polished or raw stones from local vendors to support the local economy.
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