Please help identify green rock.

[Suzanne]

This rock was in my brother's collection, I'm not sure if he collected it, or if he purchased it. If he found it himself it could be from anywhere in NY, PA area mostly, but possibly along the east of USA all the way to Florida, sorry I can't narrow it down)

It is various shades of green and grey green or white with some small orange/brown areas. The surface is covered in dark green ball shapes with tiny sparkeling crystals. Other areas are geode like with tiny brighter green crytals bordered with rings of teal green and whitish green. There is a layered chalky looking surface on some of it, but it is hard not soft like calk, although there are some tiny round bits crumbling off.

Hope the photos help, they are the sides of the same rock.

Thanks

 

[adam]

I`m going with Malachite on this one. It may also be pyromorphite 

[Suzanne]

10 hours ago, adam said:

I`m going with Malachite on this one. It may also be pyromorphite 

Thanks Adam,

I looked at pictures of both and the malachite looks the closest. I stumbled on one photo of malachite that was the most like my rock and it was called "botryoidal malachite chrysocolla". Googling that gave me many examples that are pretty spot on for what I have!

Thanks for pointing me in the right direction!

[d_day]

Yeah I'd say it's most likely malachite with crysocolla.

[4meter]

Very cool piece.  I wonder what the white, round, mineral is?  Sort of looks like Smithsonite.  The green mineral has an unusually high luster to it, more than I would expect from Malachite.  I'm not writing off Malachite but I wonder if it is not another copper mineral.  Does the high luster green mineral fizz in dilute HCl?

[Suzanne]

On 10/29/2018 at 12:01 PM, 4meter said:

Very cool piece.  I wonder what the white, round, mineral is?  Sort of looks like Smithsonite.  The green mineral has an unusually high luster to it, more than I would expect from Malachite.  I'm not writing off Malachite but I wonder if it is not another copper mineral.  Does the high luster green mineral fizz in dilute HCI?

Thanks 4meter, I think it's the most eye catching rock that my brother had in his collection! 

I discovered that the white round mineral actualy turns green if wet, but then turns the dull chalky whitish color again when it drys.

All the different surfaces seem to soak a drop of water in like a sponge, it must be very porous or full of tiny cracks and veins that the water wicks into.

I don't have any HCI, and vinegar had no effect, probably too weak.

The dark green mineral sparkles extremely beautifully! But the crystals are microscopic! I got some photos from my microscope.

 

[chrisski]

From high school physics, many years ago, I remember that water mixes with chemicals sometimes to make colered crystals.  I think they're called anhydrous and dyhydrates.  CaCl2 ٠ 2 H2O means the salt is somehow bound, not in a chemical reaction with the crystal.  This can be the colored crystal, once heated the water molecules are released so it is now CaCl2 + 2 H2O and the water molecules are freed (anhydrous).  Back in high school, we grew some crystals in water and they had colors, dried them overnight, and then heated the colored crystal in a flame the next day and the crystal turned white.  I remember the anhydrous crystal was always white, but not all dhydrate crystals had color, some were white.  I think desiccant acts the same way: white when new and purple or pink when its used up.

My guess us that is what you have going on here.  I don't know how repeatable this is with add water and heat to turn white and back again, but may be able to repeat this with a smaller portion of your specimen.

I think its pretty neat your specimen changed colors.

[Suzanne]

Hi chrisskit, that high school experiment sounds cool! I'll have to look up about that. I'm used to a rock getting darker when wet but it was quite surprising how much change there was in the white globular bits turning a very nice turquoise green.