In terms of category, the most common are the Five Elements Spiritual Bones as follows

1、Spiritual Bones of gold
2、Spiritual Bones of wood
3、Spiritual Bones of water
4、Spiritual Bones of fire
5、Spiritual Bones of earth

There are rare variant bones such as follows

6、Spiritual Bones of ice
7、Spiritual Bones of thunder
8、Spiritual Bones of and wind

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As for the quality grade, it is divided into four grades

1、Purple Spirit Bone
2、Gold Spirit Bone
3、Black Spirit Bone
4、White Spirit Bone

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Among them, the Purple Spirit Bone is the rarest and is also known as the Heavenly Spirit Bone,  the White Spirit Bone is the most useless.

And Mortal Bones can not cultivate immortality.