Natural amber forms are not accidental. They depend primarily on where the resin seeped out of and what shape the crevice in which it gathered had. The season of the year, exposure to sunlight (the warmer the more liquid the resin, the colder the thicker and more hardened the resin), the condition and age of the tree—all this influenced the forms of amber. The resin solidified when dripping down the bark (such pieces are known as layered amber) or as stalactites and drops falling off tree branches. It often accumulated to seal tree wounds (forming so-called “scabs”). The resin took shape underneath the tree bark (the pieces formed there are lens-shaped in their cross-section) or inside the tree trunk in so-called pockets. These pieces are flat, bent, tile-shaped or irregularly shaped. So-called moulds are the most attractive for jewellery production: they are massive barrel-shaped pieces from inside tree trunks.

When transported, the pieces lost their natural shape. Usually, they are irregular in form, being fragments broken off a larger piece or small crumbs. So-called cobbles are pieces with their surface polished by the glacier moving together with them. The original amber shapes were also altered by the movement of sea waves.

No other kind of amber has a diversity of colours equal to Baltic amber. Its vast colour range is due to the presence of fine air bubbles or organic debris—invisible to the naked eye, trapped inside the amber millions of years ago—and due to the conditions in which it was deposited. Amber is opaque if it has millions of tiny air bubbles trapped inside it, probably as a remnant of water. The most common amber varieties are yellow. White, bluish or greenish colours are rarely found. Amber is a living stone: it darkens when exposed to sunlight and air. Inside, pieces of amber are usually lighter in colour than it would seem from the tint of their outer weathered layer.

Lexicons of amber varieties based on folk terminology list about 100 terms to describe amber: bone amber, trinket, cabbage amber, sugar amber or honey amber are just some of them. Amber can be transparent, translucent and opaque, in rich shades of yellow, red, brown, beige but also white, bluish or greenish, with these colours sometimes making up unique mosaics. Pure pieces, but also those filled with fine plant matter which is arranged in intricate and unique patterns, cause admiration among amber enthusiasts.