Twannberg is a rare Iron meteorite classified within the IIG group, discovered in the Twannberg region of Switzerland. Formed over 4.5 billion years ago within the metallic core of a differentiated asteroid, it represents one of the few known examples of the uncommon IIG classification. Twannberg is particularly significant due to its unusual chemistry, including elevated phosphorus content and distinctive trace element composition, which set it apart from more common Iron meteorite groups. Its recovery from glacial and sedimentary deposits in the Jura Mountains has also contributed to its scientific and historical interest.

Twannberg specimens are composed primarily of iron-nickel metal and often display coarse crystalline structures when cut and etched. Many pieces show well-developed Widmanstätten patterns alongside inclusions of phosphide and sulfide minerals, reflecting their slow cooling history within an asteroidal core. Surface preservation varies depending on the specific find location and weathering history, but prepared specimens can reveal striking metallic textures and structural detail.

Studying Twannberg provides valuable insight into the formation and evolution of rare Iron meteorite parent bodies, particularly those with unusual chemical pathways. As one of the best-known IIG Irons, it has played an important role in refining understanding of this scarce classification group. For collectors, Twannberg is highly desirable due to its rarity, European provenance, and scientific importance. Each specimen represents a genuine fragment of ancient planetary core material preserved from the earliest stages of solar system history.