Rainbow obsidian

Rainbow obsidian was an obsidian variety with bands of color. It could be used just like black obsidian to make arrowheads and weapons.

Description
Rainbow obsidian was black or gray with bands of all colors except yellow. The bands could be thin or quite wide and sometimes the stripes were broken up into spangles. These stones were usually tumbled into irregular shapes for jewelry, but like black obsidian it was hard and brittle and rarely used in items that received shock or wear. A typical specimen had a base value of 50 gp.

Powers
Rainbow obsidian could pass through the various prismatic spells without harm and could grant the same protection to other inorganic materials that were connected to it. Thus, an arrow with a rainbow obsidian head could strike through a prismatic wall.