Mica Rock Samples. 10 specimens. Call 1-800-411-DINO (3466) for volume discounts. Mica is a mineral name given to a group of minerals that are similar in their physical properties and chemical compositions. They are all silicate minerals, which means that chemically they all contain silica(SiO4). Mineralogists call micas sheet silicates because their molecules combine to form distinct layers. These layers can be seen in muscovite mica specimens because it can be split (mineralogists call this feature cleavage) into very thin, flexible, transparent layers. This physical property is so distinctive that all minerals that cleave in this fashion are said to have micaceous cleavage.