...as if there was any doubt.
A local shop had some pretty rocks with fluorite crystals (note on them says "Fluorite NM" but I don't know where in NM they were collected). The others might have been more spectacular but I wanted this one (which was my Christmas present from my husband) because it had three different minerals that form isometric crystal structures. That means that they form (or can form) perfect geometric cubes. The white crystals are calcite (CaCO3), which has a hexagonal crystal structure, and I think if you zoom in on the bottom half of the rock there are some sorta hex shaped white nuggets. But no one cares about the calcite. So... the fluorite crystals (CaF2) are the clear purple/blue cubes. There are also galena crystals (PbS), but they are hard to see in this picture. Galena is super showy. The crystals look like perfect little metallic cubes with mirror-shiny faces. Most of the galena crystals in this rock are fractured, but the cube shapes still show clearly.
Well... I've now convinced myself that the glittery black crystals are not what I thought they were, (darn you, internet!) but are actually also galena crystals (I thought they must be chromite but I couldn't find *any* images of actual cubic chromite despite the fact that it's isometric.) The galena crystals have glittery coatings of Anglesite on them... PbSO4... so, essentially the surface of the galena crystal has oxidized and recrystalized as little lead sulfate crystals. Which I suppose is also pretty cool.
(The amazing box that I'm using to prop up my rock was a gift from my daughter who made it in wood shop.)
A local shop had some pretty rocks with fluorite crystals (note on them says "Fluorite NM" but I don't know where in NM they were collected). The others might have been more spectacular but I wanted this one (which was my Christmas present from my husband) because it had three different minerals that form isometric crystal structures. That means that they form (or can form) perfect geometric cubes. The white crystals are calcite (CaCO3), which has a hexagonal crystal structure, and I think if you zoom in on the bottom half of the rock there are some sorta hex shaped white nuggets. But no one cares about the calcite. So... the fluorite crystals (CaF2) are the clear purple/blue cubes. There are also galena crystals (PbS), but they are hard to see in this picture. Galena is super showy. The crystals look like perfect little metallic cubes with mirror-shiny faces. Most of the galena crystals in this rock are fractured, but the cube shapes still show clearly.
Well... I've now convinced myself that the glittery black crystals are not what I thought they were, (darn you, internet!) but are actually also galena crystals (I thought they must be chromite but I couldn't find *any* images of actual cubic chromite despite the fact that it's isometric.) The galena crystals have glittery coatings of Anglesite on them... PbSO4... so, essentially the surface of the galena crystal has oxidized and recrystalized as little lead sulfate crystals. Which I suppose is also pretty cool.
(The amazing box that I'm using to prop up my rock was a gift from my daughter who made it in wood shop.)
Comments
The nomenclature is fascinating and reminds me of enzymology where everything ends in "-ase" according to what it does. In mineralogy, everything ends in "ite."
The fluorite, galena, and anglesite are firm.