|How are emeralds formed?
|Question Date: 2015-02-12|
Beautiful question. It is very interesting how
different minerals and gems exhibit brilliant
colors. Let's first understand why we see color
around us. White light contains rays of all the
colors. When white light is passed through a
prism, one observes the separation of different
colors contained in white light. A substance
appears black because it absorbs all the different
colors shone on it, whereas a blue substance
absorbs everything except blue; what is left after
absorbing is what one sees as color.
Many minerals in their pristine state are
colorless, which means they do not absorb any
color. They appear transparent. But, if some
specific impurities are added to the mineral, the
compound assumes an interesting color. The
mechanism as to why a specific impurity produces a
specific color is a question often asked by
scientists, but the answer is complicated in most
cases. But, for most well-known minerals, we know
the reason why.
Emerald like many other gemstones such as ruby,
sapphire owe their color to impurities present
within them. In fact, Ruby and sapphire are
made of exactly the same material (Corundum, which
is a compound made of Aluminum and Oxygen with
stoichiometry Al2O3), but
ruby appears red and sapphire appears blue. The
difference in color is due to traces of Chromium
present in ruby, whereas blue Sapphire obtains its
color from traces of Iron and Titanium impurities.
Emerald is a compound made of Beryllium,
Aluminum, Silicon and Oxygen with the formula,
The green color of Emerald is due to traces of
Chromium present in them.
An emerald is a type of mineral and there are many
different types of minerals. Nearly all the rocks
that you see on the surface of the Earth and also
the rocks very deep in the Earth are made of
different minerals. Some minerals are very common
and other minerals are very rare. To understand
this, we need to understand what minerals are.
Minerals are made from different types of atoms.
You can imagine they are made of different types
of Lego pieces. Now with Lego, two things can
happen. Firstly, imagine you have three blue
and three white Lego pieces. You can build many
different forms with them. Similarly, with the
same type of atoms, you can build many different
minerals. Secondly, imagine building a house
with Lego pieces. You can build the same house out
of blue and yellow pieces, or green and white
pieces or black and red pieces. Similarly, you can
make the same shape with different types of atoms.
This will also make different minerals. Does
that make sense? Then you can understand that
for a certain mineral to form, we need to have the
right type of atom and the right structure.
Emeralds need a type of atom which is called
Beryllium and Beryllium is very rare. Only in
few places can you get enough Beryllium together
to make emeralds. Also, in order to get the
correct structure, you need to have the correct
temperature and pressure. The temperature and
pressure increases deep in the Earth. The deeper
you go, the hotter it gets and the higher the
pressure. Emeralds form deep in the Earth in
locations that have just the right temperature and
pressure and that happen to have enough beryllium.
Emeralds are made from 4 elements that are
found deep in the Earth’s crust: beryllium,
aluminum, silicon, and oxygen. These elements
are found flowing in veins filled with hot water
called hydrothermal veins. When the conditions are
just right in these veins and the cool down, the
emerald crystals start to form. Emeralds can
also be formed in magma rather than hydrothermal
veins. A lot of the emeralds we mine today are
the result of processes that happened hundreds of
millions of years ago.
Emerald is a type of crystal of a mineral
called beryl which forms in large-crystaled
granites and some kinds of metamorphic rock,
produced by the heat and pressure deep within the
earth. Emerald is different from other kinds of
beryl (such as aquamarine) by containing small
amounts of the element chromium.
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