Carat is the term used for the measurement of the weight of diamonds and other gemstones.  The word comes from the carob seed.  A couple of hundred years ago merchants looked for something to compare the weight of gemstones with.  They finally chose the carob seed as this seed was a very consistent weight from one seed to the next.  So if a customer wanted  a gemstone  weighing two carobs seeds then another merchant would know what he wanted.  In English the word ended up being pronounced as carat.  When you see “ct” then that is an abbreviation for “carat.”  Then you might also see “TW” or “ct TW” and those mean the total weight in carats of more than one stone in a ring.

Is a one carat diamond and a one carat opal the same size? A great question and the answer is a clear NO!  The reason that gemstones are different sizes for the same weight is because some are more dense than others.  Let me explain that concept of density.  If you got a plastic bottle of water and put in the freezer the next day the bottle will have expanded and will be bigger than when you put it in there.  But it will weigh the same!  So an opal has water and air and looser mineral items inside it and will take up more space than a compact and compressed or dense diamond will.  So an emerald has a different density to a topaz or a diamond or an opal.

What about small diamonds in my ring?  What size are they?  That’s another great question.  A one carat diamond is a big expensive rock!  We all know that but what about those little diamonds that we sometimes call accent stones?  Well, we weigh them in what we call “points.”  A one carat diamond has 100 points.  So in rings we tend to have small diamonds which weigh one or two or three or more points. In the trade we say: “two pointer” or a “three pointer.”  When we see that written as part of the make up of a piece of jewellery we will often see it written as hundredths of a carat.  0.01 means one point, 0.05 means a 5 point stone and so on.  When we see a quarter of a carat we would see 0.025 carat.

However, a one carat diamond will cost a great deal more than 100 one pointers or 50 two pointers.  One carat is a big diamond and rare, but little chips made into one pointers are not rare at all even though the quality might be the same as the big diamond.

Opals are an exception.  We still use carats but anything under a carat we usually break down into tenths.  So we might say an opal weighs 0.4 carats.  We would not call it a 40 pointer like we might for a diamond.  We would say an opal weighs 2.65 carats if we were being precise.

Finally, you might see a piece of jewellery weighing five carats.  That will mostly mean the total weight of the piece of jewellery the metal plus the gems.  Then you might see that you can get it in 14 carat gold or 18 carat gold.  That’s carat gold and that’s another story so don’t confuse that with the carat weight of the gemstones.