If you see two people walking and holding hands, you perceive that they are a couple because of the gestalt principle of

Proximity

Proximity occurs when elements are in place together. This is usually perceived as a group. This is usually done when objects/person are in close proximity unity occurs. This is because the eye differentiate an object from the surrounding area. When objects are place without proximity. They will be perceived as separate objects. Proximity can be applied even if there is variation in sizes shape and even if it is radically different.

The best way to tell its true color is to look at the minerals streak

Allow large amino acids through