Ruby Cube and Reflection

Create your basic cube shape and shade red.

With the cubes selection showing great a new group, and then hit the mask icon ( highlighted in green ). Since you have a selection it will automatically choose to show all contents of that group within the selected white area only.

Create an oval which will be the gloss. Fill with a white gradient almost all the way but leaving a slight bit transparent as 'falloff'.

You can see your new oval may go outside of the masked area but will only show on the canvas within the white areas.

Lower the opacity on the layer and set blending mode to Screen. You should have something similar to above.

On the cube layer set the blending options to something similar to above this will create the 'chiseled bevel' look

We will now darken the edges giving the ruby more depth. Also embossing which will make it appear like a light is shining on the top left side.

Merge all layers building up the cube, duplicate the cubes layer then use the transform tool to flip it upside down. Then using the mask technique shown above use a gradient black which will hide most of the second cube creating a relfection.

Using a round brush or gradient create what will be the shadow.

Use the transform tool again stretch and position the shadow below the cube.

Lower the opacity or fill on the shadow layer.