It is always fun to discover a new look and this was called a Black Amethyst Cluster in a waterfall formation. Gorgeous tiny crystals that sparkle delightfully. The yellow I think is limonite.
You will enjoy it more through this video. You can read more about the shape.
This crystal has many qualities in common with the purple crystals like good psychic protection. In addition, the black stones have a good grounding vibration and an excellent healer that helps rejuvenate your entire system. The yellow adds optimism and self-belief.
Contrast this black amethyst cluster with bright colours or consider earth colours for grounding harmony.