Skills (Crystallization) (Spoiler)
Crystallization Upgrade is a Bonus skill that increases the rate at which Magic crystallizes into Magic Crystal.
For the Magic crystal to change colour the crystal should be on your body and you should be the one who dealt the last blow to a monster.
Normally for the colour change and price of the Magic Crystal the below table can be considered.
Black: No magic
Red: 10 monster defeated
Purple: 100 monster defeated
Blue: 1000 monster defeated
Green: 10,000 monster defeated 1 Gold
Yellow: 100,000 monster defeated 10 Gold
White: 1,000,000 monster defeated 1 purple
Which basically equated to 1 monster = 1 nar
Now the BP addition follow the same double rule as Equipment BP addition.
First is The level of rarity. (This is the required BP). [This is the total amount of BP used to reach that level] {Skill Effects}
Level 1 = (1) [1] {2x Increase}
Level 2 = (2) [3] {4x Increase}
Level 3 = (4) [7] {8x Increase}
Level 4 = (8) [15]. {16x Increase}
Level 5 = (16) [31] {32x Increase}
Level 6 = (32) [63] {64x Increase}
For eg. : Suppose the skill is at Level 6 and you kill 1 monster, so the Black Stone will change to Red as it will be like you have killed 64 monsters instead.
CREATORS' THOUGHTS 
Avi2112
Avi2112 The Final form of Crystals will be Infinity stones :p
Weekly Power Status
-- Power
Ranking 
-- Power
stone