One of the many activities that visitors and Haida Gwaiians like to do on island is to search for agates. "Agate is a microcrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks."(from Wikipedia). Agates are a result of gas bubbles in lava. As the lava cools the gas escapes leaving a cavity.
Silica in solution seeps into the cavity and forms layers, gradually filling the cavity. As erosion by wind and water occurs the agate or nodule is released. Agate is translucent and relatively hard.
It shows up in various sizes and colours here on Haida Gwaii. In the photo above the big rock is opaque while the agates are translucent. The density of agates is considerably lighter than "normal rock".
Most agates found on Haida Gwaii are the size of the little ones in the forground but occasionally after a good storm some big ones will wash up on shore. The agate on the left weighs in at 6lb 2 oz and is currently being looked at for possible cutting to see what is inside. (My orange crock is size 11 for size comparison!)
This beautiful opal geode(a form of agate and quite possibly what the other big agate is) I found last week after one of our big storms.
In this case the nodule did not fill with silica before it was released from it's birthplace so crystals formed in the open space. You can see the layers of silica that formed to make this the agate.
This beach, within Naikoon Provincial Park is called Agate Beach for a reason! The two large agates I found come from ancient volcanic activity south of Tlell.
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