Obsidian. It has very fine grain or is amorphous, and it has a conchoid fracture, so it can be worked to a sharp edge and point. Gabbro, on the other hand, has a very coarse grain and it difficult to get and edge or point on at all.

According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern C---H-I-. That is, eight letter words with 1st letter C and 5th letter H and 7th letter I. In alphabetical order, they are:

conchoid

According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 3 words with the pattern --NCH--D. That is, eight letter words with 3rd letter N and 4th letter C and 5th letter H and 8th letter D. In alphabetical order, they are:

conchoid

honchoed

ponchoed

According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 8 words with the pattern C---H--D. That is, eight letter words with 1st letter C and 5th letter H and 8th letter D. In alphabetical order, they are:

clicheed

clochard

clubhand

clubhead

cokehead

conchoid

copyhold

crashpad

According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern C---HOID. That is, eight letter words with 1st letter C and 5th letter H and 6th letter O and 7th letter I and 8th letter D. In alphabetical order, they are:

conchoid