A tale of two ambers
From sap to rock
Since the definition of a mineral includes having both a specific chemical composition and a regular crystalline structure, amber does not qualify. Amber is fossil tree resin with quite variable composition and at best a rudimentary organization of its organic molecules.
This little wasp is only about two millimeters long. It became trapped in soft resin about 2.5 to three million years ago near what is now Moa, Tanzania.
Whether or not this is actually amber is debatable. Resin begins to lose volatiles and to harden within days to a few years, but the definition of amber is that the organic molecules must polymerize, meaning that they reorganize themselves by linking into longer strands, coincident with additional hardening and embrittlement of the material. That can take tens of thousands to millions of years to happen, and a lot of material labeled “amber” is far too young to be true amber, although it may make for better decorative items than brittle amber.
There’s an intermediate stage between resin and true amber, called copal, which strictly speaking derives from a particular Mesoamerican tree, but similar material from Africa, used as incense, is also called copal along with similar material from around the world. In the 18th to early 20th Centuries, East African copal was used extensively as a component of furniture varnish.
My specimen in the photo is old enough to be amber, but young enough that it might still technically be copal. I’ve seen it called both in professional papers, but copal is most likely. Regardless, the cool thing about it is obviously the well-preserved 3-million-year-old wasp trapped in it. Cat. No. 174.
Here’s another tiny critter in the same piece as the wasp.
This little beetle (Coleoptera) in amber is from the Dominican Republic where the amber is dated uncertainly, to 15 to 40 million years old, from Miocene back into Eocene time. The original label said it was from family Anobiidae, the family of wood-boring beetles (and certified by Dr. Robert Woodruff, a Florida State University entomologist).
It looks to me to be a Chrysomelid, the group including leaf beetles, but 1) I’m no beetle expert; 2) this little thing is barely more than a millimeter long, and not especially well preserved; and 3) there are something like 1.5 million beetle species. But still, it’s an insect several million years old!!
The earliest known fossil beetles are from the Permian, about 295 million years ago. The amber-bearing sediments from the Dominican Republic appear to be from brackish to swampy environments into which rivers brought blobs of tree resin. The resin, probably from deciduous trees similar to acacias, washed into material that became lignite, the first stage of coal formation (Stach and others, 2021, The study of Dominican amber-bearing sediments from Siete Cañadas and La Cumbre with a discussion on their origin: Scientific Reports volume 11, Article number 18556).
There was likely a fairly dense forest of acacias that dropped resin into streams or directly into an adjacent lagoon, where rapid burial preserved the resin and let it convert to amber (Iturralde-Vincent, 2001, Geology of the amber-bearing deposits of the Greater Antilles: Caribbean J. Sci. 37, 141–167). Iturralde-Vincent also thinks the abundance of amber in the Dominican Republic was related to a warm, moist climactic optimum about 16 million years ago, but again I don’t think the age of this amber is very well constrained.
Cat. No. 212