Holypie Wrote:can a black crystal give attack on an armor?
According to JMS, no. Both black and dark crystals effect STR, INT, DEX and LUK according to the following chart:
| Crystal | Low Range | High Range |
| Low Black | -1 | 1 |
| Mid Black | -2 | 2 |
| High Black | -3 | 3 |
| Low Dark | -2 | 2 |
| Mid Dark | -3 | 3 |
| High Dark | -5 | 5 |
I'm aware this is slightly different from Isaac's explanation of the dark and black, so either one of is wrong, or it's implemented differently between versions.
To answer the root of your question - Only sapphires and diamonds are restricted to weapons.