A single silver diamond.
The rank typically associated with the gold leaf insignia in the army is that of a Major.
The black leaf insignia is used for the Major rank in the Army. It is all for the Major rank in the Air Force and Marines.
The hat insignia and rank insignia contain the eagle from the great seal
Very basically speaking, the difference is one step in rank. While a Lt. Colonel is normally referred to a Colonel, a Colonel is sometimes to referred to as a "full bird colonel" to distinguish the difference. In the Army at least, a Lt. Colonel wears a clover leaf rank insignia (silver, I think) but a full Colonel wears an eagle insignia, hence the reference "full bird."
Yes. Major General is also referred to as a "two star" General, for their rank insignia of two stars.
Lieutenant Colonel, the insignia is a silver oak leaf.
For the US Army, it's a bronze oak leaf. The same insignia is used by Majors in the Air Force and Marine Corps, and by those holding the rank of Lieutenant Commander in the Navy and Coast Guard while wearing certain uniforms.
A cadet is a student not a rank
No
Cadet Colonel / Cadet LTC
For which service branch? For US Army ROTC and JROTC, it's a single silver diamond (or subdued if worn on the ACU uniform). It varies for other branches.
Lieutenant Colonel insignia is identified by a Silver Maple Leaf. In the US Army it is a cluster of silver OAK leaves. In the British army it is a crown and a single 'pip'.