While the concept of a geode planet, where the surface is made of rock but the underground is filled with precious gems, is intriguing, it is highly unlikely to exist in reality. Here's why:
Formation of Gems: Precious gems, such as diamonds, emeralds, and rubies, are formed under specific geological conditions, involving immense pressure, temperature, and specific chemical compositions. These conditions are typically found deep within the Earth's mantle, where the appropriate environments for gem formation exist. The surface of a planet, however, is generally composed of lighter materials like rocks and soil, lacking the necessary conditions for gem formation.
Surface and Mantle Composition: Planets, including Earth, are formed through complex processes such as accretion and differentiation. During these processes, heavier elements, including gems, tend to sink towards the core, while lighter materials rise to the surface. Therefore, it is highly improbable for precious gems to be concentrated near the surface of a planet, as they are more likely to be found deeper within the mantle or core.
Rarity of Precious Gems: Precious gems are called "precious" precisely because they are rare and valuable. If they were abundant in large quantities on the surface or in the underground of a planet, their value would significantly diminish. The scarcity and desirability of precious gems are closely tied to their geological rarity and the difficulty involved in their extraction.
Geological Processes: Geological processes, such as erosion and tectonic activity, tend to bring materials from the underground to the surface over time. If a planet had a subsurface rich in gems, these processes would likely expose some of those gems on the surface through natural geological activities. Therefore, the existence of a planet with a surface devoid of gems but a subsurface filled with them is highly unlikely.
While it is fascinating to imagine a planet adorned with precious gems, the geological processes and conditions required for such a scenario make it improbable. However, there are other celestial bodies in the universe, such as asteroids or moons, where rare minerals and gems may be found in more concentrated forms due to their unique formation and history.