Final answer:
In an amethyst geode, the mineral crystals are typically well-formed, indicating a euhedral shape due to slow cooling rates allowing for unhindered growth.
The correct answer is 4.
Step-by-step explanation:
The size of mineral crystals is influenced by the speed of cooling, with slower cooling rates allowing the crystals to grow larger. Therefore, the appropriate term to match with the letter for crystal shape in the context of a geode would be Choice 1: A-euhedral, B-subhedral, C-anhedral. An euhedral crystal has well-formed crystal faces, a subhedral crystal has partly formed faces, and an anhedral crystal has poorly formed or no crystal faces. Considering an amethyst geode, which exhibits clear pointy crystals, Choice 1 with A-euhedral seems the most appropriate match, as these crystals typically form with well-defined faces in a relatively undisturbed environment allowing for unhindered growth.