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Identity HelpUnknown Plumas Co. Ca. rock

1st Aug 2020 05:21 UTCBrad von Dessonneck

Hello all,

I recently found this rock in a pegmatite in Plumas County, California, near Antelope Valley Reservoir. I am thinking that it is quartz (lt brn/clear) and possible garnet or rutile (dark red) oriented in the same direction. Possibly due to parallel growth. There is a dark red crystal that I believe is a garnet in the photo (lower left side), and minor plagioclase.

The piece is about 5 cm long and the rough specific gravity is about 3.21. It was found in a quartz vein with plagioclase and minor dark mica. Rose quartz is also known from this area. The host rock is a granodiorite.

Thanks!

1st Aug 2020 05:25 UTCBrad von Dessonneck

Here is a close up of the texture. I was unable to figure out hardness since the grains are so small.

1st Aug 2020 05:28 UTCBrad von Dessonneck

one more photo. Hope these help.

1st Aug 2020 06:38 UTCHerwig Pelckmans

Hi Brad,

Contrary to popular believe, even small grains can be used to do a hardness test.

Here is how:

You only need one small grain and a scratch free surface of for example a knife blade.

Hold the knife blade horizontal and mark a small (scratch free!) area with a permanent marker. Then put the grain on the knife blade and put one of your fingers on top of the grain. Now push hard on the grain and slide it back and forth over the blade a few times. Remove the grain (put it somewhere safe for other tests) and wash off the knife blade. Then look with a hand lens to see if the grain has scratched the knife.

The remainder of the story, as well as the use of other materials with diffferent hardnesses, is obvious.

Also, isolate another grain of the unknown and crush it. Then pour the powder on a sheet of white paper and see what color the powder has. Let us know that color.

Cheers, Herwig

ACAM & MKA

1st Aug 2020 20:40 UTCSteve Federico

Dear Brad,a red streak means you followed bad advice and sliced your finger open.Glad I'm not an expert.

2nd Aug 2020 07:27 UTCHerwig Pelckmans

Haha, Steve, great humour!

Sure you must be an expert in that!

Cheers, Herwig

ACAM & MKA (Belgium)

4th Aug 2020 01:47 UTCBrad von Dessonneck

Hi Herwig and Steve,

Thanks for the advice. It scratched a knife but not quartz, and the powder was a light reddish-brown (no blood!). It as difficult to separate such small crystal grains.

I am leaning towards rutile with quartz now, but my pegmatite mineralogy is not very strong.

Photo of a 1-2 mm wide grain.

Thanks again,

Brad

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