Sphene vs. Demantoid part 2
I also forgot what I was going to talk about relating to the title of that last entry, so here's part two.
So, the sphene I saw today was fucking spectacular. And huge. And the dematoids in that earring were small. And maybe I haven't seen a dematoid as large and as skillfully cut as that one was, but as I was brushing up on where demantoid sits on the dispersion index chart, I was ABSOLUTELY CERTAIN that sphene was higher than demantoid. Except it wasn't.
So it goes like this:
Sphalerite 0.156
Demantoid 0.057
Sphene 0.051
Diamond 0.044
I know these numbers mean nothing to you, but colored light can be measured by these numbers, and these numbers just shows who has a higher dispersion. Sphalerite has nearly three times more colored light that reflects back than a Diamond.
I was shocked that Sphene really was below Demantoid. There's no way. That fucking thing sparkled RED.
So I was like, "Maybe it has a higher refraction and it tricked me into thinking it had a higher dispersion..."
Refraction:
DIamond 2.417 - 2.419
Sphalerite 2.368 - 2.371
Cassiterite 1.997 - 2.098
Demantoid 1.88 - 1.94
Melanite 1.88 - 1.94
Sphene 1.843 - 2.11
Huwhat?! Sphene is five places below diamond?! WTF.
Okay, yeah, the high range in Sphene goes all the way up above Cassiterite's highest refraction... but they are still ordered highest to lowest... I wonder if there is a mean or a median average or where they typically hit. How is it that Sphene looks SO MUCH MORE DISPERSIVE than Demantoid?!
Turns out Sphene is birefringent and Demantoid isn't. Birefringence is when a wave of light goes into the stone, splits into two, and is reflected back and different rates. If you look through a birefringent stone at a lined piece of paper, the lines will be doubled.
That's got to be it. I had never paid attention to that before in stones. I could decipher if a stone was what it was purported to be by how colorful-sparkly or white-sparkly it was or wasn't, and I knew about the existence of birefringence but I hate physics. Ugh, now I have to learn physics!
Its amazing how gemstones keep me on my toes in geography, chemistry, AND physics. And then there's the quality of a stone cut which gets into geometry. I should be able to sight-identify the quality of a stone cut by its proportions. I have, of course, read all these things and the history and theory of optimal stone cuts, but I can't look at a stone and be like, "The table of this stone is about 58% of its width and therefore optimal for the return of light." or whatever the heck. I should be able to make at least a general assessment like that by sight. I guess in talking it out, I know the things that go into this kind of sight-identification, its just that I don't actively think about it when I'm looking at stones unless it is something that jumps out at me - either in that it is high in quality or low in quality. Like, "Boy, this is a really shittly cut stone since I am getting no refraction" or "there's a dead spot" or "I can see right through this like glass" or "I can see flashes of color I don't normally see in this type of gem but it's cut so well that it maximizes its dispersion." or whatever.
I love gems.
So, the sphene I saw today was fucking spectacular. And huge. And the dematoids in that earring were small. And maybe I haven't seen a dematoid as large and as skillfully cut as that one was, but as I was brushing up on where demantoid sits on the dispersion index chart, I was ABSOLUTELY CERTAIN that sphene was higher than demantoid. Except it wasn't.
So it goes like this:
Sphalerite 0.156
Demantoid 0.057
Sphene 0.051
Diamond 0.044
I know these numbers mean nothing to you, but colored light can be measured by these numbers, and these numbers just shows who has a higher dispersion. Sphalerite has nearly three times more colored light that reflects back than a Diamond.
I was shocked that Sphene really was below Demantoid. There's no way. That fucking thing sparkled RED.
So I was like, "Maybe it has a higher refraction and it tricked me into thinking it had a higher dispersion..."
Refraction:
DIamond 2.417 - 2.419
Sphalerite 2.368 - 2.371
Cassiterite 1.997 - 2.098
Demantoid 1.88 - 1.94
Melanite 1.88 - 1.94
Sphene 1.843 - 2.11
Huwhat?! Sphene is five places below diamond?! WTF.
Okay, yeah, the high range in Sphene goes all the way up above Cassiterite's highest refraction... but they are still ordered highest to lowest... I wonder if there is a mean or a median average or where they typically hit. How is it that Sphene looks SO MUCH MORE DISPERSIVE than Demantoid?!
Turns out Sphene is birefringent and Demantoid isn't. Birefringence is when a wave of light goes into the stone, splits into two, and is reflected back and different rates. If you look through a birefringent stone at a lined piece of paper, the lines will be doubled.
That's got to be it. I had never paid attention to that before in stones. I could decipher if a stone was what it was purported to be by how colorful-sparkly or white-sparkly it was or wasn't, and I knew about the existence of birefringence but I hate physics. Ugh, now I have to learn physics!
Its amazing how gemstones keep me on my toes in geography, chemistry, AND physics. And then there's the quality of a stone cut which gets into geometry. I should be able to sight-identify the quality of a stone cut by its proportions. I have, of course, read all these things and the history and theory of optimal stone cuts, but I can't look at a stone and be like, "The table of this stone is about 58% of its width and therefore optimal for the return of light." or whatever the heck. I should be able to make at least a general assessment like that by sight. I guess in talking it out, I know the things that go into this kind of sight-identification, its just that I don't actively think about it when I'm looking at stones unless it is something that jumps out at me - either in that it is high in quality or low in quality. Like, "Boy, this is a really shittly cut stone since I am getting no refraction" or "there's a dead spot" or "I can see right through this like glass" or "I can see flashes of color I don't normally see in this type of gem but it's cut so well that it maximizes its dispersion." or whatever.
I love gems.