Trays are an unusual cave formation formed from clusters of popcorn which ends in a flat-bottomed surface. They often have aragonite trees growing beneath them, as in the photo below, taken in Lechuguilla Cave. Trays are generally calcite, but can also be formed in gypsum.
The origin of trays is complex. They usually form on ceiling pendants, with aragonite frostwork first forming along the edges where undersaturated water flows down the pendant and evaporates. Water rising in the frostwork by capillary action causes the frostwork to grown upwards and lateral, creating the flat-bottom surface. Over time, the frostwork dissolves and is redeposited as calcite popcorn, due to the relative differences in the solubility of calcite and aragonite.

AUTHOR: Dave Bunnell