Stalactite slice coffee table

A complete polished slice across a stalactite or stalagmite, with a brown centre and then bands of brown, cream and green agate edged with tiny whitish quartz crystals.  It is on a frosted glass pedestal base and is a good height for a coffee table.  Do you know how to tell a stalactite from a stalagmite in situ? A stalactite has to hold on tight, a stalagmite might reach the roof.  

Maximum 3 3/16 inches (8.1 cm) wide, 2 1/8 inches (5.4 cm) deep and 1 9/16 inches (4.0 cm) tall.