Gem people call this Moonstone.
Moonstone is a member of the feldspar family, a really broad family of minerals which are contained in Granites and of gem size in Pegmatites.
Feldspars are aluminium silicates of Sodium, Potassium or Calcium.
Other well known minerals in the Feldspar group are Labradorite, Albite, Sunstone and Aventurine and Orthoclase.
Gem quality Moonstone can be found between Hughendon and the Lynd in Queensland at a place called (wait for it!) Moonstone Hill.
The property that gives Moonstone and some other minerals a cat or tiger eye appearance is called chatoyance. Moonstone is a mixture of Albite and orthoclase and during cooling of the magma those minerals separate into crystalline bands giving Moonstone its chatoyant property. Other minerals that can display chatoyance are Sapphire (Star sapphires), aquamarine, labradorite, beryl, quartz (tiger eye).
Feldspars are the most abundant rock forming minerals and compose over 50% of the earth’s crust but pure and clear gem quality specimens are rare.
Realised the topic was show and tell and I had only shown, so thought I’d do a little research. Good to learn a bit.