FMF - Friends of Minerals Forum, discussion and message board

[Philippe Durand]

it will make my day, chipped or not.... Just a dream

[bob kerr]

[RayStraw]

Bob:

I have examined the specimen pictured and believe the reflections on top are all remnants of the original azurite crystal because all contain steps parallel to the other relected azurites. The steps between these relected azurites indicate that the original azurite was steped on its faces.
I believe it would be hard to nucleate new azurites on a malachite pseudomorph surface with all in the same orientations to each other.

I would welcome any other interpretation to these azurite remnants.

Ray Straw

[Peter Megaw]

I agree with the argument that this is not simple epitaxy, but for these to be remnants of a hackly shell of azurite, somehow left behind as the body of the crystal was replaced from within...an unorthodox and a counterintuitive mechanism... requires that the evidence all support that model. The individual azurites appear almost crystallographically oriented...but several features indicate they are secondary to the malachite.

1. If the malachite was replacing an earlier azurite stage, why would the edges and crystal faces around each azurite remain not only unreplaced, but seemingly untouched by malachite replacement? We can't see it all, but it is hard to believe that all the azurite on all its faces would escape being touched.

2. From simple paragenetic cross/cutting relationships it appears that the azurite overlaps and sits higher/above the malachite...indicating it is later and was not there to be replaced by the malachite.

3. Areas of individual crystals that are optically/crystallographically continuous/members of a single larger crystal "colony" are quite common. Sand crystals are one example, as are fluorites that grow on top of heavily coated fluorites that nonetheless have continuity at a very fine scale with the material below/lateral to them are also common. Somehow crystals can grow in lateral continuity over considerable distances and "through" various obstacles that look obvious to us, but that the crystals ignore.

4. If this reflects unreplaced azurite with a hackly multi-faceted crystal surface, why do we not see surfaces like that on unreplaced crystals? I can't claim to have seen all th Milpillas azurites around, but that is not a texture I have seen on a pristine azurite.

I have to agree with Bob that these sure look like an azurite stage growing on/after the malachite pseudomorphed an earlier azurite stage.

[RayStraw]

Thank you for your take on this issue.

Ray Straw

[Birdbrain59]

Whatever it may be it’s a gorgeous specimen.