Gemstone Refractive Index And Refractometer Mini-Quiz

If you’ve made it through our 3-part refractometer guide for gemologists, test your knowledge of refractive index (RI) analysis with this mini-quiz. Click on the link at the end of the quiz to see the correct answers. Got some wrong? Check out the refractometer review section below.

1. Parallax is caused by

  1. Double refraction
  2. A facet not being flat
  3. Lenses that need cleaning
  4. All the above
  5. None of the above

2. If you use a red filter with your refractometer, you need to make an adjustment to your reading of

  1. -0.005
  2. +0.589
  3. Neither
  4. Both

3. If you’re testing a gem and measured a high RI of 1.612 and a low RI of 1.608, the stone’s birefringence is 0.004.

  1. True
  2. False

4. A moderate-sized spinel inclusion in a spinel host gem will have a significant effect on its value.

  1. True
  2. False

For the answers, click here.

Refractometer Review

Question 1

Parallax is an optic effect that looks like the cutoff line wavering between scale divisions. It’s caused by a non-flat facet. Parallax is a common occurrence in refractive index testing that can be confused with an indication of gemstone birefringence.

Question 2

A refractometer should be calibrated at …

Premium Article

This is a Premium Article. Please become a member to read this entire article and gain access to hundreds more like it.

Membership options

Full Article Details

Content Length 451 words
Reading time 2 min 15 sec

Here's what you get if you unlock this article:

  • Refractometer Review
    • Question 1
    • Question 2
    • Question 3
    • Question 4

Plus, additional member-only benefits:

  • Exclusive access to other premium articles and courses
  • Unlimited access to our gem pricing guide
  • Participate in our member-only forums
Membership options