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Red Chatoyance in Crystal Opal

I have this piece of unimpressive semi-crystal, semi-white opal that
I cut thin, about 2.5mm thick. It has a yellow tinge to it as much
Australian opal has.

It is an oval about 25 x 15 mm. It has a little green and blue fire
in it. But what I haven’t seen before quite like this is a line or
a point of bright red light that runs across the stone as it shows
in the light source.

It turns up in incandescent, and halogen as well as in sunlight.
The odd thing too is that it stays opposite the reflection of the
light source. So that with the sun shining on the top of the cab
there is a white reflection of the sun on the surface of the oval on
one side of the cab and then there is the bright red pinpoint on the
opposite side of the top. It depends on the flatness or roundness of
the surface whether it is pinpoint or line of red.

Another color peculiarity of this stone is if I let the sun shine
through it, the color of the light on the other side is a bright
golden yellow. In fact I can see through it and it turns the light
orangish yellow. AS I’ve looked at it, more one additional thing
that is odd. When the sunlight shines through the stone onto white
paper, if forms a long feather ended light shape, I guess it’s
refraction, that is yellow/orange. The oddity is that the length of
the light shape is opposite the length of the cab. The long side of
the cab forms the short refraction light shape.

Sorry about how complicated this description is. I’ll try to
photograph this all if anyone wants to see it.

So has anyone seen this sort of thing before? Would you know what
is causing the red?

Derek Levin