A mineral's true color is observed by...

A mineral's true color is best determined by conducting a streak test on unglazed porcelain tile. The streak test involves rubbing the mineral against the tile, which allows you to observe the color of the mineral in its powdered form, often revealing a more reliable and consistent color than what you might see on the surface of the mineral itself. Surface coatings, impurities, and other factors can affect the observed color of the mineral when viewed in its natural state, but the streak reflects the mineral’s inherent color.

Other methods, such as using a colorimeter, involve more complex instruments that measure color more quantitatively and might not be as straightforward or as practical for identifying minerals. While comparing to a color chart can provide a reference, it does not guarantee an accurate representation of the true color due to variations in lighting and mineral quality. Likewise, viewing the mineral under different lighting can lead to variations in appearance that do not reflect its true color. Thus, the streak test remains a reliable method for determining the true color of a mineral.