Here's why:

* Pearly Luster: Mica often exhibits a pearly or iridescent luster, especially when viewed from certain angles.

* Conchoidal Fracture: Mica breaks with a conchoidal fracture, meaning it breaks into smooth, curved surfaces that resemble the inside of a shell.

Other minerals that could potentially fit this description are:

* Talc: Talc also has a pearly luster, but it's much softer than mica and breaks with a more uneven fracture.

* Gypsum: Some varieties of gypsum, particularly selenite, can have a pearly luster and conchoidal fracture, but it's not as common as with mica.

To be sure, you'd need to consider other properties like hardness, color, and streak. But based on your description, mica is the most likely candidate.