Ammonite

Ammonite polished ammonium horn cephalopod

Millions of years old
Origin Madagascar

Size approx. 21 x 17 cm, it weighs about 1.9 kg

You buy exactly this shown ammonite

You buy exactly this pictured ammonite, which even opalesces red,
opalescent ammonites are also called ammolite

Ammonites belong to the group of fossils (petrifactions).
Fossils are imprints or remains of plants and animals of earlier geological epochs.
Ammonites are cephalopods with spirally coiled shells.
Since many fossils were once used worldwide for cultic and medicinal  purposes, quite a few synonyms exist: Ammon horns, ophites, saligrams, snake or snail stones.