The term 'SILICA GEM' is a combination of two words, 'SILICA' and 'GEM'. SILICA is a mineral composed of silicon and oxygen, and is the most abundant mineral in the Earth's crust. Gemstones are precious or semi-precious stones that are cut and polished for use in jewelry. The crossword solution for the term 'SILICA GEM' is 'OPAL', which is a type of gemstone composed of hydrated amorphous SILICA. Opals are known for their unique play of color, and are often used in jewelry.