How does the surface of a refracting prism become reflective?

[Browntown]

Homework Statement: How does the surface of a refracting prism become reflective?
Homework Equations: None

In my physics lab, we placed a mirror in front of a telescope with built in crosshairs and crosshairs that were shining out the front of the telescope which reflected against the mirror and allowed us to see them and then adjust the level of the telescope until the two were aligned. Later we had to do the same but with the surface of a refracting prism where once the telescope was pointed at a specific angle, the surface became like a mirror and allowed us to align the crosshairs.

In order to fill in the theory section I need to understand how this occurs but I have no idea other than there is some kind of total internal reflection happening.

Any help understanding would be much appreciated, thank you.

 

[jedishrfu]

You can have both refraction and reflection occurring at the same time.

http://www.differencebetween.net/science/difference-between-reflection-and-refraction/
However, based on the angle of incidence the refraction component may disappear:

https://www.physicsforums.com/threads/refraction-object-disappearing-in-liquid.948029/