Sillimanite Al2SiO5 (in schist)
Would you have guessed that these three disparate minerals all have the same chemical formula? The three minerals are all polymorphs of Al2SiO5. They exhibit the widely varied forms, dependent on the temperature (x axis) and pressure (y axis) at formation.
The crystal systems of the minerals vary from kyanite's triclinic to andalusite and sillimanite's orthorhombic crystals. In particular a variety of andalusite called chiastolite shows these marked crosses:
The distinctive blue of kyanite, from the Greek meaning "deep blue" shows different hardnesses in different directions.
And sillimanite occurs in metamorphic schists formed at relatively high temperatures and pressures.
A Plume friend was wearing a "kyanite" necklace which brought back my final mineralogy project on the KAS polymorphs...and reminded me of our final exam. We were all given different pieces of wallpaper and were to describe the symmetry of the design. It was quite a surprise and one of the exams from which I learned the most!
Your swatches of wallpaper (not the computer kind) will be winging their way to you soon:
And for extra credit, 2 advanced wallpapers
Looking forward to mineralogy, petrology, and symmetry discussions with you,
Whoa--check out this visual representation of the first 1000 digits of pi after the decimal point. That's YOUR WALLPAPER to analyze ;-
Gotta love Wyoming, where the signs point out geologic formations and their ages:
Does your state do this?!