Question

Realgar and orpiment are both minerals of arsenic (As) and have the same chemical composition. Which one of the following properties can be used to distinguish between the two minerals in hand specimen?

• A. Lustre
• B. Hardness
• C. Colour
• D. Fracture

Answer 1

The Correct Option is C

To distinguish between realgar and orpiment, which are both minerals of arsenic with similar chemical compositions, we need to carefully consider their distinguishing properties. The options given are lustre, hardness, colour, and fracture. Let's analyze these options:

1. Lustre: Both realgar and orpiment have a similar glassy to resinous lustre, making it difficult to differentiate between them based on this property alone.
2. Hardness: The hardness of these two minerals is quite similar on the Mohs scale, typically around 1.5 to 2. This makes hardness an unsuitable property for distinguishing them.
3. Colour: Realgar and orpiment have distinct colours. Realgar is typically red to orange-red, while orpiment is yellow. This colour difference is the most reliable property to distinguish between the two.
4. Fracture: Both minerals typically exhibit conchoidal to uneven fracture, making fracture not very useful for differentiation.

Considering the above analyses, colour is the property that can be used to distinguish between realgar and orpiment in hand specimens. Realgar's red to orange-red hue contrasts with orpiment's yellow, making colour the obvious distinguishing feature.