This is a polished marble of a pallasite – a type of stony-iron meteorite, consisting mostly of centimeter-sized olivine crystals. Olivine is a silicate mineral often found in the Earth’s mantle.
Pallasites were once thought to originate at the core-mantle boundary of differentiated asteroids that were subsequently shattered through impacts, but that theory has been replaced recently by another one, which claims that they are impact-generated mixtures of core and mantle materials