NOT Calcite in Decorative Lava Rock

So I found this decorative lava rock in the yard, and noticed that it had some crystalization on it that I at first assumed was calcite. But it's not; it's waaaay too hard (hardness around 6 or 7) and cannot be scratched with a steel blade. It's an odd peach/tangerine color which is unusual for quartz. The rock looks like the typical decorative reddish lava rocks you find in landscaping projects- except for the atypical crystalline mass. Not sure what it is; really have no idea. Probably something common I would assume, but what, exactly? Some kind of transparent feldspar? (I have heard of such a thing; isnt that basically what the Oregon Sunstones are?) Or iron-laced quartz pseudomorph of something else?

A plagioclase feldspar could certainly be possible. Does it show good cleavage planes?

Matt

It looks like an iron stained bleb (or whats left of one) of quartz in the lava rock to me.

Wayne

I think I see cleavage planes; thus I agree with Alfredo. A plagioclase feldspar? Can you see any striations on a cleavage face? They are not always visible and appear on only one of the two major cleavages. If so that would be fairly conclusive for plagioclase.



Edited 1 time(s). Last edit at 07/11/2012 04:59PM by Donald Peck.

it does look like somewhat squarish cleavage planes; particularly across the top.