FMF - Friends of Minerals Forum, discussion and message board

[Jaime_Cerdeira]

Dear all,

This is my first post here, and I'm very excited to be part of this community!

I recently discovered an ancient volcano in Lisbon that has been converted to a quarry and is now abandoned.

We can find there amazing calcite crystals formed in association with Volcanic Breccia and Basalt.

However, I've been having some difficulties in the identification process.

For you, what can we call this crystal habit?

[Roger Warin]

Hello,
These crystals are short prisms m{10-10 } with a classical termination e{01-12}}. Often it's the other way around, with the prism dominating and the rhombohedral termination only appearing later. The prism is then elongated.
Well done for your research.
There are over 300 different forms of calcite...

[Jaime_Cerdeira]

Dear Roger, thank you so much for the reply!

I leave here more examples that I collected there!

The crystal habit appears to be botryoidal with some linear formation

Best regards.

[Jaime_Cerdeira]

This one seems to be lamellar?

[Roger Warin]

Since no one answers, because the photos are not expressive, I suggest that it is the same previous habit in which the prism has disappeared.
This calcite would therefore only be made of the rhombohedron e{01-12}.
It is not lamellar, but the rhombohedron is very obtuse.

[Jaime_Cerdeira]

Hi,

Thanks again!

But this time I was asking for the calcite that as been covered in iron oxides (orange).

In this location, there is a lot of different crystal habits.

Best regards.

[James Catmur]

I think that is what Roger is talking about. It is the same crystal habit