Let's go over what we know about color.
Sunlight is made up of lots of different colors
all mixed up together. Light can either be
reflected or can pass through things. Different
colors might be reflected or transmitted
differently, too. An example of this is a prism.
A prism takes white light and transmits each
different color slightly differently. This
ends up spreading the white light out into a
rainbow. Not surprisingly, a rainbow is made when
light from the sun is transmitted through drops of
water differently, causing the different colors to
For snow to be white, it means that it must be
reflecting all the different colors of light
equally. For ice to be clear, it is transmitting
all the colors of light equally and not reflecting
them back to your eye. To understand where the
difference comes from, we need to think about the
structure of snow. Lets start with ice. Ice isn't
really as transparent as a pane of glass. If you
look through an ice cube, everything looks kind of
murky. This is because the ice is bending the
light a little bit -- it doesn't pass through the
ice in a straight line -- and so things get
blurry. Snow is made completely out of a bunch
of tiny flakes of ice. So when you are looking
at a snow bank, you are looking at a bunch of tiny
ice flakes and a whole bunch of air that fills the
spaces between the snow flakes. Since it snow
flake is ice, it will bend light passing through
it slightly. This light will hit another flake,
then another, then another, and bounce around
randomly from flake to flake until it eventually
comes right back out again. Some of the light does
get absorbed by the snow but a lot of it comes
Since snow doesn't distinguish between all
the different colors of light, they all get
reflected back and so the snow appears white.
So here is a question for you: What happens if
you take an ice cube and you start scraping off a
pile of ice flakes? Would the pile look
clear like the ice cube or would it look white
like snow? Actually, if you have a really
large chunk of ice (for example, a glacier) you
will notice that the ice looks a little blue, not
clear. This is because ice absorbs red light
better than blue light. As light travels through
the ice, it has less and less red in it but the
same amount of blue, so it appears bluish.
I believe the difference is that snow is made
up of a bunch of small water crystals where big
blocks of ice are not. All the crystals in the
snow would tend to reflect the light in all sorts
of directions with the net effect that a lot of
the light that hits a pile of snow is
reflected, making the snow look white.
With ice, more of the light is transmitted
through which makes the ice seem colorless.
An even more dramatic example is the difference
between diamonds and graphite, both are carbon.
Diamonds have a crystalline structure and tend to
reflect light in interesting ways. Graphite does
not have the same crystal structure and looks
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