If you are into collecting prism tiles, here is a tough piece to add to your repertoire:

1901 Luxfer Skylight Tile, 6 1/2" squared, light purple. Two flakes off of the corners, light scratches.

Embossing: LUXFER 98...

Very few have been salvaged from old buildings. This tile originated from the Chicago Loop area. Don't snooze!

$300 shipped & insured.