Final answer:
Biotite and muscovite micas exhibit a sheet silicate structure, where silica tetrahedra are connected in very thin layers, giving these minerals their characteristic flexibility and sheen.
Step-by-step explanation:
The micas, including biotite and muscovite, have a unique silicate structure known for its sheet-like form. In these silicate minerals, the basic building blocks are silicon-oxygen bonds configured into silica tetrahedra. These tetrahedra connect to each other in very thin layers, creating a structure that is notably flexible and elastic, which gives micas their characteristic wavy layers with sheen.
This type of structure classifies them as having a 'sheet silicate' structure, as opposed to other structures such as single chains, double chains, three-dimensional networks, or independent groups.