Op 29-10-2021 om 02:05 schreef Samuel B.:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> Correct. This needs a good knowledge of crystallography indeed. I am a
>> layman on this really...
> 
> It doesn't really take any in-depth knowledge. Just a bit of time reading and
> browsing through images of minerals. (Which might be too time-consuming,
> depending...)
> 
I just browsed through the one (microscopy) crystallography book I still 
have. Principal cleavage plane is indicated as (001), meaning the 
horizontal plane.

>>> And then there are clouds... Similar to fractures, the clouds you see in
>>> minerals are often reflective/refractive gas or liquid pockets, and so they
>>> might not easily be replicated with scattering media. (...)
>>>
>> Inclusions, yes. Scattering media is a poor substitute. There are the
>> little foreign grains that got included, and the fluid inclusions. Those
>> are really interesting!
> 
> Yeah, there are many fascinating inclusions that can occur in minerals. I
> remember seeing a photo of some white crystals occasionally found in obsidian.
> IIRC, they formed in groups of four tetrahedral crystals meeting at their
> corners. Pretty much like the first iteration of a Sierpinski tetrahedron. If I
> come across the image again, I'll post it. (Image search isn't turning up
> anything relevant, and I originally found it in a book.)
> 
>> [Aside] in a very distant past, my wife did a study on fluid inclusions
>> in quartz crystals from Greece. She could, by cooling the crystals in
>> liquid nitrogen and then slow heating, determine the original
>> temperature of the liquid in which the crystal grew. Original pressure
>> was somehow derived from other factors. I forgot. [/Aside]
> 
> Crazy! I haven't a clue how those environmental factors could possibly be sussed
> out. That's hacking, as far as I'm concerned... Physical hacking, not digital,
> which is even cooler. She sounds like an awesome woman :)
> 
Ah! but she is of course! :-) She didn't remain in the Earth science 
world however, and switched to French literature (as she is French 
herself, that was a natural if not the most easy choice here in NL).

>> But, those fluid inclusions are difficult to model. I was thinking about
>> clouds of bubbles in liquid (there are a couple of scene files drifting
>> around in the pov world; I think I have a couple of those somewhere)
>> using a gaussian distribution scheme...
> 
> Inclusions are pretty much the main impediment to making better mineral renders.
> 
> And inclusions take on many forms. Not all exhibit crystalline features when
> viewed with the naked eye (e.g. light reflecting at certain angles only). Some
> do, though. I had (or still have) a Herkimer 'diamond' that apparently has an
> inclusion in the shape if a tiny quartz crystal. The bubble really looks like a
> tiny, doubly-terminated quartz crystal. I'll have to take a photo of that.
> 
>>> Besides the symmetry, another thing I noticed about the crystal libraries in KS
>>> is that the secondary and tertiary faces (modifications) tend to be somewhat
>>> exaggerated. (...)
>>>
>> Yes, I have been wondering about that. Not being an expert, I have been
>> hesitating between the different models proposed.
> 
> Eh, nothing is written in stone. (Haha, except stones.) But there are always
> outliers to these things. Depending on the conditions in which a chemical is
> grown, modifications may become more or less prominent. You never know.
> 
I am going to experiment different paths...

-- 
Thomas

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