Rocks with two different size grains of the same mineral are called porphyritic.

Here's why:

* Porphyritic texture: This texture describes rocks that have larger crystals (phenocrysts) embedded in a matrix of much smaller crystals (groundmass).

* Same mineral: The key to being porphyritic is that the phenocrysts and groundmass are made up of the same mineral.

Examples of Porphyritic Rocks:

* Porphyritic granite: Large crystals of feldspar (phenocrysts) in a matrix of smaller quartz and feldspar crystals (groundmass).

* Porphyritic basalt: Large crystals of olivine or pyroxene (phenocrysts) in a matrix of smaller plagioclase feldspar and pyroxene crystals (groundmass).

Let me know if you want to know more about porphyritic rocks!