Ashley notice that the mineral appear metallic under the light. What property was actually measuring?

 The property is called Luster

Explanation:

Luster is a term used to describe the appearance of  light from the surface of the mineral when it reflects light. The two types of classification of Luster is Mettalic or Non Mettalic.

some examples of minerals with mettalic lustre are --- Galena, graphite, Gold, Silver, Copper etc

Some examples of minerals with non mettalic lustre are--- Barite, Serpentine, Fluorite etc.

Lustrous property

Explanation:

Materials like metals that have lustre usually glow or display sheen when light comes in contact with the surface of the material.

It is derived from the Latin word "lux" meaning "light", which is indicative of radiance or gloss.

Lustre is a common property of metals, including sonourousity, malleability and ductility amongst others.

answerlinnaeus;