Muscovite after Andalusite

Unknown Owner

A grouping of blocky large crystals of what were once andalusite, these now replaced by muscovite. The specimen comes with an antique label as shown at the end of the video and dates to the early 20th century. An interesting pseudomorph specimen for this area.A pseudomorph forms when one mineral replaces another while preserving the original crystals external shape. In the case of muscovite after andalusite, the original andalusite crystal formed first in metamorphic rock. Later chemical alteration caused the andalusite to break down and be replaced by muscovite mica. The resulting specimen keeps the crystal shape of andalusite even though it is now composed of muscovite.