Show your Star sapphires and rubies

[Starstruck8]

An unusual star sapphire from central Queensland. Light brown translucent body with a gold star. In real life, the stone looks cleaner and the star looks clearer that in the pictures. I have no idea what causes the weird waviness.

13.0x11.8mm

The doubling in the right pic is caused by a strip of darker material (?hematite). This picture shows the strip and a similar plate at the right. Both are flat; they look curved because of refraction by the dome,

 

[LilAlex]

An unusual star sapphire from central Queensland.

Wow that's awesome! Looks almost metallic!

 

[Pumpkin Sparkles]

@Starstruck8

I love the waviness, almost looks like a galaxy within the stone! This is magnificent.. to those with a vivid imagination like myself this would keep me occupied just looking at it lol

 

[TeaGlutton]

I love it, it's like golden hour as seen from under the surface of the water!!

 

[Starstruck8]

So now I have some answers. It seems that the stone is a 'natural doublet' with the star-forming material at the back. The dome makes the star yellow, but it is not star-forming itself.

The plates in the lower picture in my earlier post are star-forming. (You can see this in the top right picture.) It seems that there is also a star-forming layer below the plates, not visible in the pictures.

In a stone like this, with the star formed at the back, the star moves more with movement of the lighting than in a normal star stone, with the star formed close to the surface. Here is a comparison with a normal star sapphire:

In the normal stone, the star centres move about 1.3 time as much as the surface reflections. (The theoretical ratio is 1/(ri-1), which is about 1.31 for corundum). In the new stone, In the new stone, the star centres move about 1.9 times as much as the surface reflections.

I love the waviness, almost looks like a galaxy within the stone!

it's like golden hour as seen from under the surface of the water!!

At least part of the waviness is caused by the 'bumpy' surface of the dome, which is not so well cut. You can see this in the lower pic in my earlier post - the reflections have wavy edges. So it really is like looking through a swimming pool! But I'm not sure that this is the whole story.

Looks almost metallic!

Yep, it's one of those bronzed Aussies you may have heard of.

 

[Starstruck8]

Yet another star sapphire. This is not really a good stone. The star is bright and sharp and there is interesting zoning. But the body is darkish greyish blue and opaque, so the star is on the surface only. One day I will get a star stone that ticks all the boxes...



The sharp star allows an interesting demo. If you have looked at star stones, you will have noticed that the star seems to float above the surface, as if the stone had a higher dome. Why so? Because the star moves in the opposite direction to the viewing position. So the star seen by your left eye is to the right of the star see by your right eye. So, with binocular vision, the star appears closer than the stone. If you close one eye, the effect disappears.

Here is a demo with the stone and lighting fixed, and the camera moved between shots. It's set up for cross-eyed stereo viewing (i.e., with the right-eye picture on the left and vice versa).

(If you are not used to cross-eyed stereo viewing: Hold up a finger between you and the screen. Move it so that with your left eye, it appears to point just below the long ray in the right picture, and vice versa). With both eyes, look at your finger. You should see a blurry merged stone behind it. Then bring the merged stone into focus without uncrossing your eyes and take your finger away.)