Back to the Variolites

Variolites, Olympic Peninsula, WA

I was back on the Elwha River again yesterday, documenting the amazing restoration project underway there after the removal of two old, salmon-proof dams.

(To learn more, go to:  http://en.wikipedia.org/wiki/Elwha_Ecosystem_Restoration)

In the meantime, however, I always had an eye out for one of my favorite rocks - the Variolite, a rare altered basalt associated with the Crescent Formation.

This is not a lapidary stone - it does not take a good polish, but it is rare and unusual enough, that I collect them whenever I see them. In France, they are considered medicinal and just quite possibly spiritual. Who knew?

Geology 101 Redux

Variolite "Cross-section" - Elwha River

One of my favorite finds from my search for variolites on Sunday was this fellow. About 6" inches long, it shows the distinctive feldspar "dots" of all variolites, but grading dramatically in size from the bottom to the top.  Varioites are believed to form inside "pillow lavas" or basaltic lava that erupts underwater, forming unmistakable round structures visible in many NW roadcuts (especially on the Olympic peninsula). My sources tell me that the smaller dots form as the edges of the pillows, which cool more quickly, while the larger dots grow in the slower-cooled, better-insulated interior of the rock.

This makes sense to me, but whatever the explanation, I thought this sample was particularly cool...

Mystery Solved... "Variolites"

Variolite cobble, Crescent Formation, Olympic Peninsula WA

For several years I have puzzled over the origin of this stone type, which is a remarkably common component of beach gravels around the Olympic Peninsula. (See my earlier post of July 19) It is so common, in fact, that it argues for a local source.  I haven't found that source yet - but I think I have discovered what it is.
The answer came from Scott Babcock, Professor of Geology at Western Washington State University, who has studied the Crescent Formation extensively.  He proposed that they were something called a "variolite" said to be a metamorphosed basalt (possibly pillow lava).  He sent me Googling for the quite-famous (though not to me) variolites of Durance, France.  Bingo.
A quick look at some photos of the Durance rocks was all I needed - these are clearly related.  (And there is a LOT of  basalt in the Crescent Formation here.)
As I said, the outcrop source for this rock is not known, at least that I've been able to discover, but maybe one of these days...

Variolite from Maguelon, France (www.variolite.fr)

Further note : I was also able to confirm the name, and provenance of this rock with Rowland Tabor, Geologist Emeritus at the US Geological Survey and author of the Guide to the Geology of Olympic National Park. He refers to it in his book (page 67-68) as "globular devitrification structures."  Wow, that's a mouthful.  However, he wasn't able to confirm a bedrock source. That, I guess, I am going to have to find for myself!

Mystery Rocks

Mystery Rocks, Olympic Peninsula

I would love to figure out what these rocks are. I have found them repeatedly among the beach gravels of the northern Olympic Peninsula, along the Straits of Juan de Fuca, but have not managed to figure out where they are from - or what they are.  (I found them in many locations but they are especially abundant around the mouth of the Elwha River)

They are brittle but soft enough that they do not take a polish, despite the superficial resemblance to the Orbicular Jaspers (with red spots) found in the same region.  But the raised dots are odd, and I can't think what rock type these might represent.  Anyone recognize them? The matrix is grey-green and apparently crystalline, but whatever it is, it's a really distinctive rock.

No mineral value, of course, and no one is going to make jewelery from this material, but if there is a geologist out there that recognizes it, or where it outcrops, I'd love to hear about it....

POSTSCRIPT : One reader asked whether the blebs are just surface marks, e.g. barnacle scars, but I broke some open and the spots are distributed throughout the rock.

POSTSCRIPT TWO :  MYSTERY SOLVED 8/26 !  More on a later post...