Final answer:
Seed crystals are solid particles that serve as the core for the formation of ice crystals, and they can be made up of substances rich in carbon or silicates. They attract icy mantles composed of water, methane, and ammonia in the universe, and can also initiate crystallization in supercooled liquids or supersaturated solutions.
Step-by-step explanation:
Solid particles that serve as cores for the formation of ice crystals in the atmosphere are often termed as seed crystals or nuclei. These particles can be composed of various substances, including those rich in carbon (like soot) or rich in silicates (like sand). In dark clouds where molecules can form, these seed crystals can get covered by icy mantles. The most common types of ice found on these mantles include water (H2O), methane (CH4), and ammonia (NH3), all of which are made from atoms that are abundant in the universe.
These icy mantles can also facilitate chemical reactions that produce complex organic molecules. The concept of seed crystals also applies to supercooled liquids or supersaturated solutions, where these crystals can be added to initiate the crystallization process, leading to the formation of crystalline solids where atoms, ions, or molecules are arranged in a definite repeating pattern.