Hi Charlsberg and Catkin.
18a C (for Cuba) removed from the front of a resin. What's left is a gemstone/white glass
1d Maul is the synonym used for attack
11d O(scar) rips inverted, followed by a word for pulse, more usually a unit of mass.
16a An anagram of the first two words form one of the thematic individuals. RM is the abbreviation used for Madagascar.
20a compound anagram. the letters from 'a born hedonist' form 'absinthe' plus the answer. A person who hands out.