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20ct Alexandrite (Cabochon, 19.02×12.68mm, Bluish Green) vs 20ct Topaz (Cabochon, 19.37×12.91mm, Blue)


Quick summary: When looked from above (face-up position), 20ct Topaz (19.37×12.91mm, cabochon cut) appears 4% larger than 20ct Alexandrite (19.02×12.68mm, cabochon cut). See below how they compare side-by-side on a ring and finger.

20ct Alexandrite (cabochon cut)
vs
 20ct Topaz (cabochon cut)
bluish green
 
blue
19.02×12.68 mm 19.37×12.91 mm
actual size
Actual size of 20ct Alexandrite (cabochon cut, 19.02×12.68mm, Bluish Green color)   Actual size of 20ct Topaz (cabochon cut, 19.37×12.91mm, Blue color)
 
Actual size is set for screen
Ring: Skin tone:
Ring width: 3.0 mm
Left finger image
Ring on left finger
Bluish Green 20ct Alexandrite (cabochon cut, 19.02×12.68mm) on a left ring and finger
64 mm
Right finger image
Ring on a right finger
Blue 20ct Topaz (cabochon cut, 19.37×12.91mm) on a right ring and finger
Your settings
Ring
 Gold
Skin tone
 Light
Ring diameter
 16.9 mm
Ring width
 3.0 mm
Finger length
 64 mm
Finger coverage
 76% vs 77%
Saved...
Ring diameter: 16.9 mm
USA UK Asia EU1 EU2
Actual sizes of 20ct Alexandrite Cabochon (19.02×12.68mm, Bluish Green) and 20ct Topaz Cabochon (19.37×12.91mm, Blue) as they would appear on a ring and finger. Adjust the ring and finger size to get an idea of how these gemstones would look on your finger.

Where to buy?

For certified gemstones, high-end gemstone jewelry, and birthstone jewelry, see Blue Nile

Face-up Size

All things being equal, Alexandrite will face-up smaller than Topaz for a given carat weight, because it has higher specific gravity (3.73 vs. 3.53 - this means it's "heavier" compared to Topaz of the same size). Face-up size also depends heavily on the proportions of the cut.

Face-up area is a measure of the size of the gem when viewed from above (as set in a ring). It tells you how big the gem is at the girdle plane.


20 Ct Alexandrite (Cabochon) 20 Ct Topaz (Cabochon)
19.02×12.68 mm vs 19.37×12.91 mm
197.76 mm²   205.05 mm²
Face-up size outline for 20ct Topaz (19.37×12.91mm, cabochon cut)
Face-up size outline for 20ct Alexandrite (19.02×12.68mm, cabochon cut)
20ct Alexandrite Cabochon (19.02×12.68mm)
20ct Topaz Cabochon (19.37×12.91mm)
Difference: 4% (7.29 mm²)
20ct Topaz (Cabochon, 19.37×12.91mm) has approx. 4% more face-up area than 20ct Alexandrite (Cabochon, 19.02×12.68mm).


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