What are the rulings concerning the inheritance of a grandfather in Islamic Sharia?

A grandfather is of two types: a true grandfather (jadd sahih) and a uterine grandfather (jadd rahimi). A true grandfather is one in whose lineage to the deceased no female intervenes (e.g., the father of the father). He is among the Ashab al-Furud (recipients of fixed shares) and has three situations: 1. He inherits one-sixth as a fixed share (fard) when there is a male lineal descendant. 2. He inherits by 'asabah (residuary heirship) if the deceased has no lineal descendant whatsoever. 3. He inherits by both fard and 'asabah if there is a female lineal descendant. In this case, he takes one-sixth as a fixed share and the remainder by 'asabah.

A uterine grandfather is one in whose lineage to the deceased a female intervenes (e.g., the father of the mother). He is considered among Dhawu al-Arham (relatives by kinship).

A grandfather differs from a father in that the father is not excluded, whereas the grandfather is excluded by the father. They also differ in the issue of the mother's one-third share, and in the exclusion of brothers and sisters.