t oz:

A troy ounce (t oz) or (toz) is a unit of measure used for weighing precious metals that dates back to the Middle Ages.
Originally used in Troyes, France, one troy ounce is equal to 31.21 grams, according to the U.K. Royal Mint.


ct:

The carat (ct), is a unit of mass equal to 200 mg (0.2 g; 0.007055 oz) and is used for measuring gemstones and pearls.
The current definition, sometimes known as the metric carat, was adopted in 1907 at the Fourth General Conference on Weights and Measures, and soon afterwards in many countries around the world.
The carat is divisible into one hundred points of two milligrams each. Other subdivisions, and slightly different mass values, have been used in the past in different locations.

In terms of diamonds, a paragon is a flawless stone of at least 100 carats (20 g)



By the way, this app is useful for converting amounts from Carat to Troy Ounce and vise verse.