Black plume!

Based on the appearance of the rock in the image, it looks like a type of agate, specifically a Moss Agate or Fortification Agate. Here's why:

Coloration: The rock has a mix of translucent to semi-translucent areas with inclusions of various colors, including brown, black, and some hints of yellow and green. This is typical of agates which often have colorful inclusions due to the presence of different minerals.
Patterns: The patterns in the rock, including the banding and the moss-like inclusions, are characteristic of moss agate. Moss agate is known for its green, brown, or black inclusions that resemble moss or foliage within the stone.
Translucency: The rock has a somewhat translucent quality, especially around the edges, which is common in agates due to their silica composition.

Agates are formed from silica-rich water depositing layers in cavities within volcanic rocks or other types of rock formations. The specific patterns and colors depend on the minerals present in the water during the formation process.