To find the surface area (SA) of a cube, you can use the formula:
\[ \text{SA} = 6 \times l^2 \]
where \( l \) is the length of one side of the cube.
In this case, the length of each side of the cube is 3 cm.
So, plugging in the value:
\[ \text{SA} = 6 \times (3 , \text{cm})^2 \] \[ \text{SA} = 6 \times 9 , \text{cm}^2 \] \[ \text{SA} = 54 , \text{cm}^2 \]
Thus, the surface area of the rock sample is \( 54 , \text{cm}^2 \).