FMF - Friends of Minerals Forum, discussion and message board

[Nick_Huntington]

Hello, I found these last year while doing some work in a vineyard near Lake Sonoma. The reddish areas have a waxy luster and a streak that is reddish brown (was hard to get it to leave a streak).

I chipped off a piece from a larger rock I couldn't get loose and had to leave there. The chipped off piece has a lot of different things going on with it. That photo is of the freshly exposed side. The other side of it is similar to the look of the other samples.

The different pieces I found have slightly different heft to them and I have gotten specific gravity calculations from 3.4 to 4.1.

There are some old manganese prospects in the area and several outcroppings of chert with black manganese oxides on the property so I was guessing this is one of the manganese silicates for the areas with red/pink/yellow color but unsure of what the small grey/black crystals are. Any thoughts about what minerals are making up these rocks would be welcome.

Thanks,

Nick Huntington

[Jordi Fabre]

Massive minerals and rocks are not easy to determine Nick. We can say a lot of guesses but just by a photo and without distinctive details I'm afraid that you need go to some Show or mineral club close your area and ask there if some one is familiar with what you have.

[Bob Harman]

Agree with Jordi. Also, being rocks and not a mineral, specific gravity and streak have little meaning as they are meant primarily for minerals.
Bob

[Bob Carnein]

You need to try the streak of the black mineral. My guess is that it will turn out to be hematite, which has a red-brown streak.