It’s the effect from when the metal in the core cools down ~1°C every 1000 years. They are octahedrons (like raw diamonds).
These are my two favorites: Unclassified from northwest African continent, weight 42.53 grams. Part of the surface shows fusion due to heat caused by entry into our little planet's atmosphere. Iron meteorite from Argentina (Campo del Cielo meteorite); weight 26.61 grams. This one has been polished which greatly enhances the ability to "see" the metal and the formation thereof.
This is a common piece of Stardust that got cooked in our atmosphere. A friend that collects coins gave it to me a few months back. Here is a product that fellow meterorite enthusiasts may find useful: