In situ Baltic amber is found within the Prussian Formation, with the main amber bearing horizon being referred to as "Blue Earth", so named due to its glauconite content.

The formation is exposed in the northern part of the Sambia Peninsula in Kaliningrad.

[1] Numerous extinct genera and species of plants and animals have been discovered and scientifically described from inclusions in the Prussian Formation.

[3] Inclusions of insects make up over 98% of the animals preserved in the amber, while all other arthropods, annelids, molluscs, nematodes, protozoans contribute less than 0.5% of the animals.

Vertebrates are another 0.5% of the animals included and mostly are represented by mammal fur, feathers, and reptiles.