Gemology Certification Data Analysis & Decision Making 2 — Questions and Answers
Question 1: A gemologist records the following refractive index readings for five stones: 1.544, 1.548, 1.543, 1.546, 1.544. What is the mean RI?
- 1.544
- 1.545 (Correct answer)
- 1.546
- 1.543
Correct answer: 1.545
The mean is (1.544+1.548+1.543+1.546+1.544)/5 = 7.725/5 = 1.545.
Question 2: When plotting specific gravity values on a scatter chart, which axis conventionally represents the measured variable being tested?
- X-axis (horizontal)
- Y-axis (vertical) (Correct answer)
- Z-axis (depth)
- Either axis is acceptable
Correct answer: Y-axis (vertical)
In scientific data plots the dependent or measured variable is placed on the Y-axis by convention.
Question 3: A buyer receives 20 diamonds graded VS1 by one lab and SI1 by another. What is the BEST first analytical step?
- Average the two grades
- Re-examine each stone under 10× loupe to compare inclusions (Correct answer)
- Accept the higher grade
- Reject all 20 stones
Correct answer: Re-examine each stone under 10× loupe to compare inclusions
Examining inclusions directly allows the gemologist to understand the discrepancy before making any commercial decision.
Question 4: Which statistical measure best describes the spread of fluorescence intensities across a parcel of 100 diamonds?
- Mean
- Mode
- Standard deviation (Correct answer)
- Median
Correct answer: Standard deviation
Standard deviation quantifies how spread out values are around the mean, making it ideal for describing variability in a dataset.
Question 5: A gemologist plots UV fluorescence intensity versus color grade for 50 diamonds and sees a downward trend. This relationship is best described as:
- Positive correlation
- Negative correlation (Correct answer)
- No correlation
- Causation confirmed
Correct answer: Negative correlation
A downward trend between two variables indicates a negative correlation.
Question 6: Which tool is MOST appropriate for tracking daily weight calibration drift of a precision gem balance over one month?
- Pie chart
- Run chart (time series) (Correct answer)
- Histogram
- Frequency table
Correct answer: Run chart (time series)
A run chart plots measurements over time and is ideal for detecting drift or trends in instrument calibration.
Question 7: A lab receives a sapphire with an RI of 1.762–1.770. The birefringence is 0.008. Which conclusion is supported by the data?
- The stone is likely glass
- The data is consistent with natural corundum (Correct answer)
- The birefringence rules out corundum
- The RI indicates synthetic spinel
Correct answer: The data is consistent with natural corundum
Natural corundum (sapphire) has RI 1.762–1.770 and birefringence 0.008–0.010, so the data fits perfectly.
Gemology Certification Data Analysis & Decision Making 2
A gemologist records the following refractive index readings for five stones: 1.544, 1.548, 1.543, 1.546, 1.544.
What is the mean RI?