A 2.5 carat opal can be anything from less than 200.00 to over 2,000.00. The value will depend on several things such as cut, and pattern.
you first must know the color of the Opal (i read this on a website called opal.com)
If someone was trying to obtain an Opal ring that was made with 14 carat gold they could purchase one at a jewelry store. Opal rings can also be purchased online through a variety of online stores.
Black Opals are rare. Depending on the size, oval shape, etc. the value of a black opal can be listed at approximately USD $1000 per carat.
A common misconception. Carat is nothing to do with size. Carat is related to weight and therefore a 1 carat stone depends on the gemstone in question and its cut. 1 carat is 0.2g and a 1 carat round-cut diamond is approximately 6.5mm in diameter. Similarly, since CZ is a diamond simulant, a 1 carat round-cut CZ is also deemed to be one that is 6.5mm in diameter but such a stone actually weighs more than 0.2g because CZ is more dense than diamond.
Three carat diamonds weigh three carats: that's how 'big' they are.
That depends on the cut, carat, color and clarity. For e.g, a round 1 carat D color, IF clarity, and an excellent cut diamond costs about $11, 081 and a 1 carat marquise diamond with the same characteristics costs about $17, 066, both of which are GIA certified.
If the opal has fire, play of color, it is used for jewelry. Very little gem quality opal is imported by the USA. Most of it goes to Asia. The white opal you are used to seeing in the stores is not considered gem quality in the trade. Gem quality opal can cost thousands of dollars a carat. Opal can be man made. It is produced for research to see if it can be more efficient in transmitting light than optic cable.
A 1.00 point diamond is one carat, so a .12 point diamond is a little over 1/10th of a carat.
1 carat = 200mg
may be around 1 inch diameter size. 60 grams
Carat is a weight, so its weight is one tenth of a carat or one tenth of .20 grams.