Why is Carbon both Diamond and Graphite?

I'm pretty sure it is the way carbon is arranged which changes its form. For example, in a diamond carbon molecules are perfectly geometrically aligned. But I'm not 100% sure.

Graphite is the only non-metal form to conduct electricity. This is because the atoms are aligned in 'planes', therefore delocalized electrons are able to pass through the structure.

Diamond however takes advantage of carbons 4-bond capability to form a giant tetrahedral structure. 1 carbon is bonded to 4 other carbons and so forth.

Just a correction to evil dead, graphite is the only non-metal ELEMENTAL form that conducts electricity to a substantial degree. (everything can conduct electricity a little bit)

Why does graphite have a different atom structure than diamond?

Look at the following and you can see the structures of both.
giant covalent structures

This explanation from the ElementSix website:
"Synthetic single crystal diamond has an identical physical structure to that of natural single crystal diamond. The basic diamond atomic structure, described by its unit cell can be pictured as a face-centred cube (as shown below) with a carbon atom in the middle of each face and four more atoms arranged diagonally opposite each other in pairs, with the upper plane offset at a right angle to the lower plane. Unlike graphite, the individual planes are not flat but corrugated. In diamond, each carbon atom is connected to four other carbon atoms by covalent bonds. In the simplest case, these four atoms form a perfect tetrahedron. Due to covalent bonding between the atoms there are no free electrons and synthetic diamond is normally not electrically conducting. In the case for synthetic diamond, one or more of the carbon atoms might be replaced (or substituted) with nitrogen atoms, giving the diamond a yellow colour."
What is the atomic structure of Synthetic Single Crystal Diamond?

Showoff >_>

:-p

Dude . If you didn't know then simply don't post. Quoting large sections from a website isn't helping. Don't do it next time.

This is an 'Ask ME' Helpdesk, not a 'please-quote-large-sections-for-me' helpdesk. If the person asking the question wanted quotes he would have done it himself.