Dominican amber

[2] However, other authors have suggested a date in the Miocene, around 20–15 million years old, based on marine microfossils found in the sediment the amber is contained in.

In the northern area, the amber-bearing unit is formed of clastic rocks, washed down with sandstone fragments and other sediments that accumulated in a deltaic environment, even in water of some depth.

[4][5][6] In the eastern area, the amber is found in a sediment formation of organic-rich laminated sand, sandy clay, intercalated lignite, and as well as some solvated beds of gravel and calcarenite.

Since the holes are situated high on mountainsides and deep inside said mountains, the temperature is cool and bearable, but after several hours the air becomes stale.

The holes fill up quickly with water, and there is little point in pumping it out again (although sometimes this is done) because the unsecured walls may crumble.

[10][11] The blue amber reportedly is found mostly in Palo Quemado mine south from La Cumbre.