Mobs can't move on amethysts

This bug report is a parity issue with Java.

Summary:

Mobs can't walk on amethysts (of any stage). This does not correspond to the Java version.

Steps to reproduce:

1. Make a 3x3 block platform with amethysts.
2. Summon a mob on the central block.

Observed results:

The mob cannot walk.

Expected results:

Mobs must walk on amethysts just like normal blocks.

Video:

Produce_4.mp4