Well-formed staurolite crystals are commonly twinned, crossing at at 60° or 90° angles, that are called fairy stones or fairy crosses. I found this pair of staurolite twins in a streambed, where the sugary muscovite, feldspar and occasional small garnets around it were being eroded away. Large, clean staurolite specimens are found near Taos, New Mexico.
Staurolite is fairly hard, measuring 7 to 7.5 on the Mohs scale, and is used as an abrasive mineral in sandblasting.