- A mineral is a kind of object
- The luster of an object can be determined by looking at that object
- Therefore, the luster of a mineral can be determined by looking at it

So, the luster of a mineral can be determined by looking at it
Question
Which property of a mineral can be determined just by looking at it?

Context
- A mineral is a kind of object 
- The luster of an object can be determined by looking at that object