Tuesday, October 25, 2011

Our World Tuesday ~ Agates

 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.
 The is the source of most of agates found on Haida Gwaii, Tow Hill.  Tow Hill is the the lava flow of an ancient volcano.  The left side of the volcano has eroded into the sea exposing the dolomite columns.  As the sea batters and erodes the exposed dolomite nodules or agates are released to be tumbled and washed ashore on the beach.
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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6 comments:

Gaelyn said...

Nice finds. I used to gather agates on some Oregon & Washington beaches.

Pierre BOYER said...

Great and lovely...
Regards from France,

Pierre

lgsquirrel said...

This was like a magazine quality article with both fascinating information and great pictures to illustrate it. To have a beach of those stones? Wow.

Judy said...

Thank you! I learned a lot today! I love the second photo, where the translucent agate sits on top of the opaque beach stone!!! Beautiful!!

Powell River Books said...

When my parents would take me camping in the summers (they were both educators so that's when we all had time off), we would go to Oregon. Some of the beaches there had agates, but nothing like the ones you find. I always was thrilled to find one that was as big as my thumb nail. I guess they just grow things bigger in Haida Gwaii. - Margy

Kay said...

Wow....your agates are huge! I found a pretty big one on our recent trip there in August. I posted a pic on Erica's facebook wall.
Hope you & your family are all well.
Take care,
Karin

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