Lapidary / Gemstone Community Forum

Stone Talk / Moderator, Hummingbirdstones ( Robin ) => Rough on the bench and slabs off the saw (general minerals board) => Topic started by: Ryaly2dogs on April 08, 2016, 08:15:42 pm

Title: Plasma Agate
Post by: Ryaly2dogs on April 08, 2016, 08:15:42 pm
Hi folks:  Fresh off today's Friday saw are a few slabs of what the locals call plasma agate.  Provenance is Clear Creek in Central California in mountain range between King City east of Highway 101 and Coalinga off Highway 5 on the east.  Rock locale is very close to mercury mine (New Idira) and a benitoite mine.  Access is limited due to natural asbestos, that said, what a fun place to visit, no one there and we timed it after a moderate rainfall to keep any dangers at bay!

Still sawing up pieces after 5 months.  No two are alike, oh what fun! The red specs are cinnabar, and the blues and blacks are agatized serpentine(?) and jadeite associated with the Franciscan Formation which is in part derived from mantle materials and melange in a former subduction zone when the Pacific and North American plates collided back in the day.  Fun stuff.

As a newbie, please someone tell me if the photo actually posted (it does not show up in "preview").  thanks all.

Cheers.  Happy weekend to you all.

Title: Re: Plasma Agate
Post by: hulagrub on April 08, 2016, 09:32:19 pm
Better looking than the plasma agate i received a few years back!

Title: Re: Plasma Agate
Post by: Ryaly2dogs on April 08, 2016, 10:42:50 pm
I am curious, what did you receive a few years back and how does it compare to the posted photo.  Thanks in advance.

Title: Re: Plasma Agate
Post by: hulagrub on April 11, 2016, 08:03:54 am
I'd have to go dig it out, but it was much more bland. And it was rather fractured, I was guessing it was either blasted loose or heavy handed jackhammer.

Title: Re: Plasma Agate
Post by: lithicbeads on April 11, 2016, 05:31:47 pm
These form in faults and are extremely variable. We have similar rough here in Washington . It starts as a listwanite  in a fault ( the listwanite has a series of precursor rocks as well) and it becomes more silicified with each additional  soaking in hydrothermal solutions. Listwanites are brittle and fracture easily making easy paths for metal bearing hydrothermal fluids but  it is usually well healed when found in the field. The scientists call the green quartz a fibrous calcedony like chrysoprase. Rarely it gets to a point that it turns red. We find lots of boulders in the streams that follow the faults but we also have it in cliffs that defy rock tools. I could see people using dynamite on it in frustration but with it's inherent brittleness not a good idea.There are probably geological reports for the area giving the average metal content. One mountain of it up here is about 1% mercury.

Title: Re: Plasma Agate
Post by: Ryaly2dogs on April 13, 2016, 04:32:55 pm
Thanks for the info, lithic.  I admittedly had to look up listwanite and was pleased with the additional perspective and info, so apparently it starts out enriched in carbonates and then gets silicified? Crazy history with that rock.

Based on a day's haul at three different locations in the collecting area, I have quite and range of colors in hand.  Makes for some fun in the shop, and always an interesting time at the saw.