If geologists can't tell sometimes without rigorous analysis, than I certainly can't but two questions occur to me. How would crystals of the two minerals be interwoven or entwined? Would it be at the same time or would one be formed before the other? Also, in the photographed specimen, how have such delicate structures survive uncrushed? They look as if they would crumble to powder even if brushed with a finger!
I'm no expert on these minerals, but the chemistry is so similar, I can easily envision changing conditions of temperature, pressure, and chemical concentration so that the two minerals would indeed be crystallizing at virtually the same time. The result would probably be what we'd call "intimately intergrown" crystals, or zones, of the two minerals. If those conditions did not fluctuate a lot, but changed from one set of conditions to another, then we might have one of the minerals, followed by the other (I've seen this stuff with botryoidal balls in a core (presumed rosasite), with spikes of presumed aurichalcite growing on them). Re survivability, they might not crumble to powder, but a brush of a finger would certainly break or bend the spikes and bruise the balls. This would have grown in a cavity or on the wall of an open fracture. They are both tough enough that when the collector broke the piece off the country rock they held together, but the act of collecting certainly would have damaged or destroyed some, along the breaks or whatever. Some minerals are indeed so fragile and brittle that the act of collecting would shatter them extensively. These actually hold together pretty well unless actually touched or hit quite sharply. Lots of variation in that behavior.
Your comments regarding the difficulty in species identification when relying on color alone were spot on! Thanks for sharing.
If geologists can't tell sometimes without rigorous analysis, than I certainly can't but two questions occur to me. How would crystals of the two minerals be interwoven or entwined? Would it be at the same time or would one be formed before the other? Also, in the photographed specimen, how have such delicate structures survive uncrushed? They look as if they would crumble to powder even if brushed with a finger!
I'm no expert on these minerals, but the chemistry is so similar, I can easily envision changing conditions of temperature, pressure, and chemical concentration so that the two minerals would indeed be crystallizing at virtually the same time. The result would probably be what we'd call "intimately intergrown" crystals, or zones, of the two minerals. If those conditions did not fluctuate a lot, but changed from one set of conditions to another, then we might have one of the minerals, followed by the other (I've seen this stuff with botryoidal balls in a core (presumed rosasite), with spikes of presumed aurichalcite growing on them). Re survivability, they might not crumble to powder, but a brush of a finger would certainly break or bend the spikes and bruise the balls. This would have grown in a cavity or on the wall of an open fracture. They are both tough enough that when the collector broke the piece off the country rock they held together, but the act of collecting certainly would have damaged or destroyed some, along the breaks or whatever. Some minerals are indeed so fragile and brittle that the act of collecting would shatter them extensively. These actually hold together pretty well unless actually touched or hit quite sharply. Lots of variation in that behavior.