FMF - Friends of Minerals Forum, discussion and message board

[Ru Smith]

Meanwhile, inspired by Josele's wooden model, goes to fridge to look for model-making materials. Carrots or cheese?

[Ru Smith]

Cheese.

[Ru Smith]

The penetration twin lacked something in the execution, but the cube and cube-dodecahedral spinel contact twins came out well.

[prcantos]

Really surprising idea! These are 'gourmet twinnings'...

These examples show that twinning may be studied using abstract geometry which doesn't depend on the crystalline structure.

[Peter Farquhar]

What a great idea for learning about twinning while enjoying a pleasant snack. The opportunities seem endless. Do you recommend any particular cheese?

[Ru Smith]

Thanks gents. I honestly had fun making and eating these models. The very nice Argentinian Cabernet Sauvignon was also a good accompaniment. I had looked at the 2 year matured Reypenaer cheese, found it a bit too thin, and then decided for a good Viking cheese (Jarlsberg). How about some rutile twin models?

[Ru Smith]

I found this Cornish sphalerite twin with similarities to the Bulgarian galena twin shown earlier. It shows the 60 degree rotation of one element relative to the other with some partial interpenetration.

[Ru Smith]

This Kësterite twin is a tetragonal equivalent of a spinel contact twin. The photos are not as clear as I'd like.

[Ru Smith]

Greetings all,

I just took another look at the Naica fluorite twin, here orientating it with twinning axis vertical and playing with the lighting to highlight re-entrants. I need to try again given a spare moment, with a bit of image stacking to get more depth of field and highlighting of more faces. Compare with the "cheese model" above!

[Ru Smith]

Here's an interesting cyclic arrangement of spinel twins from Myanmar.

[Roger Warin]

What a beauty, as in textbooks.
Roger.

[Ru Smith]

Thanks Roger. As usual though it's still not as ideal as in the drawing. Here I've rotated a photo to compare with the old Dana drawing.

[Ru Smith]

While I have the camera out - a pretty spinel twin of diamond.

[Don Lum]

Beautiful diamond, Ru. I like it.

[prcantos]

This is a limburgite specimen showing some zeolite micro cystals in vugs: you can see a spinel-twinned faujasite crystal below a sharp octahedron, and some tiny offretite crystals on a spherical mineral (probably phillipsite or hyalite).