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Star Garnet

Starstruck8

Brilliant_Rock
Joined
May 13, 2021
Messages
761
I wish you would make a thread about your 4-ray star garnet! I would love to see it showing off all its axes.

As requested by @glitterata, here are some more pics of my star garnet.

Star garnets are sometimes seen as rock shop stones, especially the merely 4-ray ones. (I bought mine from a rock shop.) But they have an interesting feature. Interesting, that is, to geeks... They have six star axes. So a good star garnet sphere would show twelve 4-ray stars. Low cabs usually show only one star. But high-domed cabs can show up to seven. Mine shows six (almost seven) stars. You have to turn the stone to see them all. There are the main one in the middle, two on each side, one that can be seen if you look from 'below the horizon' at one end, and one that can almost be seen if you look from below the horizon at the other end.

Here is a picture:
StarGarnetMulti.jpg
Left: the main star. Middle: one of the 4 side stars. Right: an end star. The tape is to reduce bright reflections.

A video showing a tour of six stars is probably more convincing:

So, how does this work? This article gives a good explanation, with lots of interesting pictures. Short story: Garnet has a cubic crystal structure. Star garnet contains rutile needles oriented to the four long diagonals of the cube. (The <111> directions, for crystallographers.) These give star axes in directions orthogonal to pairs of long diagonals, i.e. the directions of the octahedron edges (the <110> directions). On a sphere, the rays would cross at about 70 degrees.

The rarer 6-ray star garnets have an extra set of rutile needles oriented to the directions of the octahedron edges. The extra rays bisect the broad angles of the four-ray stars. My stone has a very weak six-ray effect. Under ideal conditions, in full sun under a blue sky, if you know where to look, if you use your imagination a bit... you can just about see it (indicated with arrows):
StarGarnetSixth.jpg

Most star garnets seem to be an opaque dark plum colour, like mine. But I have occasionally seen pictures of more translucent ones (never in person). If anyone has one of these, or any other interesting star garnets, I would love to see them.
 
Thank you, @Starstruck8 . That is so interesting! I love the video. Clearly I need to visit more rock shops!

I have a 6-ray star garnet. I'll have to take a careful look at it if the sun ever comes out again and see if I can find additional stars on it. It only shows its star in extremely bright light.
 
that is really cool :kiss2:
it wasnt until just before xmas that i only saw my very first star anything (a sapphire) in the flesh (-well cold hard stone )
rock shop finds can be really fascinating and im glad this one is wearable !
 
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