The term AGATE FORM refers to a type of rock formation that is composed of several different minerals. The crossword solutions for this term are ONYX (4 letters), STEELIE (7 letters), GEMS (4 letters), MARBLE (6 letters), PEARL (5 letters), and SILICA (6 letters). ONYX is a black or dark-colored gemstone, steelie is a type of MARBLE, GEMS are precious stones, MARBLE is a metamorphic rock, PEARL is an organic gemstone, and SILICA is a mineral composed of silicon and oxygen. All of these materials can be found in agate form, which is a type of layered rock formation.