[Rockhounds] when volcanoes drop bombs: giant crystal payload

[Lanny]

Most likely it is from the Cinder Butte cone SE of Spencer. Easy to 
find, follow the road east from Spencer past the opal deposit access 
road, when you hit the "T" turn right towards Dubois and drive down to 
the cinder cone which is in plain sight, can't miss it.

Those large plagioclase megacryst/xenocrysts are common and fairly easy 
to find in the cinders and bombs and weathered free. A few are sharp 
crystals, a few have large cuttable areas (typically pale yellow). The 
identification is given as labradorite for those on Cinder Butte and 
Mac's Butte and andesine at Crystal Butte (from Earl V. Shannon, 
"Minerals of Idaho"). Generally the information Shannon used was from 
specimens and work done at the Smithsonian, so should be reliable. All 
these cinder cones are in the same area of Idaho, east of Spencer and 
Dubois and north of St. Anthony. There are more cinder cones in this 
region and westerly to Craters of the Moon and the INEEL (Idaho 
National Engineering and Environmental Laboratory). Some are 
accessible, some are not. Could be some good "sunstone" prospecting for 
the prospector minded. Geary Murdock collected several gem quality 
sharp yellow crystals up to about 1 1/2 inches 15 years ago from one of 
the cones. One of the many things on my To Do List and I haven't gotten 
to exploring that area yet, except for Cinder Butte.

Regards,

Lanny


On Aug 1, 2007, at 8:30 AM, DonH wrote:

> Pmodreski at aol.com wrote:
>
>>  In a message dated 8/1/2007 8:06:12 AM Mountain Daylight Time,  
>> nospam at orerockon.com writes:
>> It's  sunstone, it is from a well know collecting site on a cinder 
>> cone in WY  just over the ID border.
>> Ah, but sunstone is a descriptive term, is it sanidine or orthoclase? 
>>   Probably orthoclase.  Don, the master feldsparologist, will 
>> certainly find  out.
>
>
> Holy cow, what a way to start the morning.  OK, in sum, I can say the 
> gentleman definitely found it in Idaho; so perhaps there is more than 
> one volcanic field with this type of formation?  I never had 
> volcanology so I don't know if this could have blown that far from WY.
>
> The geologist who is working with these kept calling them plagioclase. 
> But there is no point in speculation or pontification until we get a 
> chance to look at them.  He had some of them prepped for mass 
> spectrometry so I suppose he'll know the trace elements and REEs soon.
> I will try to x-ray them today but maybe someone else is using the 
> instrument.
>
>
> Don
>
>
>
> -- 
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