From Destiny 2 Wiki
Fundamental Osmium is a Planetary Material found in Savathûn's Throne World. It appears as a metallic lump of ore, with some spikes protruding from it.
Unlike other planetary materials, interacting with a Fundamental Osmium resource node does not reward an inventory item. Instead, it rewards 20 Throne World Rank reputation, which increases the player's rank with Fynch. Because of this, Loot Caches in the Throne World do not reward Osmium, and instead reward 20 Throne World Rank per chest.