In "A Golden Nature Guide"called"Rocks and Minerals" I read,
"Oriental emerald, a green corundum gem, is harder (than emerald)
and may be the most valuable gem" (page 84).
A fine example of “don’t believe everything you read”. Most
commonly, the phrase these days applies to stuff found on the web,
but published books are not immune (nor are posts here on Orchid,
including this one, for whatever it’s worth).
“Oriental emerald” is not a generally accepted name for green
sapphire. As a general observation, when a gem of one variety (such
as green sapphire) gets labeled as something else but with a modifier
to differentiate it from the real thing, it’s usually safe to assume
that what it’s trying to pretend to associate itself with, is the
rarer or more valuable gem. Citrine Topaz isn’t Topaz. It’s Citrine
quartz. But sellers switch in the word topaz because that’s usually
the more valuable gem. Likewise, a fine emerald will almost always be
substantially more valuable than a similarly looking green sapphire,
though in truth, a green sapphire with the intensity of green of a
good emerald would be quite rare (I can’t recall ever seeing one, to
be honest). The green sapphires labeled oriental emerald that I’ve
seen generally have been fairly poor quality material, a long ways
from “the most valuable gem”.
As to differentiating gems and testing them, unlike general
mineralogy, most fine gems (at least the transparent types) tend to
be single crystals, or at most, single twinned crystals. In short,
materials upon which optical tests can be performed that do no damage
to the gem. These can identify the type of mineral in the vast
majority of cases, without needing to resort to the types of “assay”
methods used with ores, which often are at least slightly
destructive. In determining things like the nature and analysis of
the impurities that can give gems their color, it’s not generally
valued to know the exact percentages of, for example, the Chromium
that gives ruby it’s red color. Determining that it is indeed
Chromium that’s doing it, instead of something else, is usually
what’s important, along with any other impurities that may modify the
appearance (such as iron altering the color of ruby, usually for the
worse) and after that, what’s evaluated is the actual color, not
usually the precise chemistry of it’s cause.
The exception is when it’s desired to determine the actual origin of
the stone, which sometimes can be done not just down to a region
where a given stone is found, but in some cases, even the actual mine
(though that’s less common.) Here, useful tools will be examining and
determining not just the impurities that give a crystal/gem it’s
color or properties, but as well, the identities and nature of the
inclusions, bits of other minerals trapped in a gem, like little
garnet crystals sometimes seen in diamonds, for example. Also, when
the exact nature of the impurities is desired, tools like
spectroscopy are often used, because these, like other optical tests,
are not damaging to the gem. There are other tools more advanced labs
can use, such as electron microprobe, x-ray fluorescence, x-ray
crystallogrophy, and more, but some of these may require at least a
small sample that is damaged in the test. Normally, the size of the
needed sample is very very small. Nothing like your suggested one
gram sample.
Hope that helps.
Peter Rowe