Friday, January 15, 2010

From the "You never know what you might find" file ...

Recently, my Field Partner, Mark, called me up and said, "Hey, lets go out to the West Side for a whole day!" He was in the middle of a 2 week vacation, enjoying his rest, his family, and his new lapidary equipment.
Of course, this suggestion was like spilling a barrel of honey in front of a black bear, and in a flash, I'd checked with my life and business partner Laura, and after admitting she could survive a daylong break from me (I LOVE YOU, Honey!), she acquiesced and the trip was set.

Now, I know I'm leaving you hanging, but I'm writing a full goose "magazine article" type Field Trip Report, so I'll leave the full trip details for later. Suffice to say that it was a truly amazing day, spent with a delightful and adventurous Field Partner.

We left before first light, and by noon, we'd visited more than 9 separate sites in 3 counties. Only one site was truly great, but we found something at all but 2 planned stops, where we ran into access problems. Yep, you guessed it, (Vermont accent, please) "You can't get there from here!"
This is, after all, California, and ALL Ranches have fences, and are generally well posted with "No Trespassing" signs.

A little after noontime, we headed toward the junction of I-5 and County Highway J1 in Western Fresno County. Heading west from the off ramp on J1, we decided to check below the dam at the Little Panoche Reservoir and see if we could find a digging site before we ate lunch.
Which we did, and along with several buckets of notable (and cuttable!) jasper and agate, I found a real "Whistler!"

The "Jello Salad" Jasper

Sticking just a thumb sized tip out of the alluvial "bank," in the right-of-way we'd found, was the stone pictured above. I'd kicked at it (Official Rockhound Collecting Technique #1) thinking that it was a less-than-usual black jasper with "spiderwebs." Basinite, as black jasper is known, isn't unusual for this area, but we seldom find it with quartz stringers.

After a couple of minutes of uncovering the piece by toe, and prying it loose with my shovel from the crusty, gypsum rich soil, this strange and wonderful stone was revealed.

"What, no walnuts?"

From the unbroken "rind" patches on the stone, it would appear that the silica gel that became jasper might have been held in a gel state long enough for mineral concentration to occur, causing the "blobs."
The other possible origin that comes to my mind is that they were brecciated material and alluvial pebbles, and were carried into the vein emplacement with the gel, which then cooled. Cracks formed during cooling, and were filled with low temperature quartz, causing the spiderwebs.

Alluvial pebbles or brecciated material?

From eyeball examination, there's little evidence of sand inclusions, though the shapes that show on the exterior are mixed, some rounded, some ragged edged. (Magnification shows that there's sand.) Perhaps the vein began as a watercourse, and underwent subduction, then was filled with the silica gel. If anyone has any other ideas, I'd love to hear them, please!

We'll be taking a "Going Home From Tucson on I-5" Field Trip back out to this area on February 27th, and anyone who wishes to come along is most welcome to attend. If you'd like to attend, please RSVP so I can bring along a special goody for you. Or, if you're not able to make that date, you can contact me at, and I'll be glad to send a Google link with map and directions to the site, or meet you if I am free on your chosen date.

Here are more pics of the "Jello Salad Jasper."


2.5 pounds of jaspery goodness!

I can't wait to slab this one!

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