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Mineral Characteristics
On this page you have the
mineral characteristics.
The typical characteristics that are used in the process of mineral identification are colour, streak, transparency, lustre, habit, hardness, cleavage, fracture and specific gravity.
Below is info about each one.
Colour
Colour
seems like a simple characteristic to use, particularly in the
beginning before you get familiar with other characteristics. My
warning is - don't trust
the colour!
It may look simple but it's one of the trickiest mineral
characteristics!
While it is obvious that many minerals have the same colour (so you do
need to use other characteristics too), it is also true that many
minerals can come in very different colours. Quartz, for example, can
be transparent, white, pink, purple, red, yellow, green, brown, grey
and black. And that's only one example (even though one of the most
extreme ones).
Black quartz. By austinevan via Flickr.com
Streak
Streak is the colour of
the powder of the mineral.
You can powder a mineral with a geological hammer, but unless it is a
very hard mineral, a far better way is to scratch the mineral against a
so-called streak plate,
which basically is the same as the back-side of
a porcelan tile. Streak is a much more reliable characteristic to use
than the mineral colour.
Mineral streak. By opacity via Flickr.com
Transparency
Transparency is
another example on mineral characteristics that can not
always be blindly
trusted. A quartz crystal for example, as already said, can be transparent, or have
any other colour which cannot be seen through. A mineral that cannot be
seen through is said to be opaque.
And a mineral which the light can pass through, but an object cannot be
clearly seen through it is called transculent.
This is basically half way between transparent and opaque. But in
combination with other properties this is a reliable characteristic.Lustre
Lustre
is a mineral characteristics that desribes whether and how light is
reflected
off a surface of a mineral. The nature of the mineral surface and the
amount of light that is absorbed determine lustre. Lustre can be metallic
(chalcopyrite), dull
(hematite), greasy
(halite), vitreous
(quartz) or silky
(gypsum).
Waxy lustre. By jeff-o-matic via Flickr.com
Habit
A
mineral habit is the one of all mineral characteristics that should,
and often is, considered
first (I didn't start the list with it because it's only obvious for
someone experienced). To identify minerals, it is very important to
know which minerals grow crystals
- not all do. Some are "massive"-
they don't indicate any shape. Others can have acicular
(needle-like), reniform
(kidney-shaped masses), bladed,
or dendritic
(plant-like shape).
Mineral habit. By Cobalt 123 via Flickr.com
Crystal
Systems
The minerals that do
grow crystals, also grow different shapes.
Crystals can be
orthorhombic,
prismatic, monoclinic, triclinic, cubic, tetragonal, or
hexagonal.
Don't let this to scare you off! It sounds complicated, but
you don't need to learn them all. You will learn a few more common ones
in practice - you will learn the hexagonal shape of quartz once you
have seen it a few times, and you will learn the cubic crystals of
pyrite, but this is all coming with experience and you don't need to
get stressed about knowing them all when you get started.
Mineral crystal. By subarcticmike via Flickr.com
Twinning
Yep,
some minerals even grow twinning
crystals - a symmetrical but
non-parallel intergrowth of many crystals. You will learn them, there
are not too many minerals that do that. One classic example is
staurolite. To study mineral crystals closely enough, you may
need a
simple
microscope
or at least a hand
lens. 
Mineral twinning. By thomasina via Flickr.com
Specific
Gravity
As
opposed to weight, specific
gravity is relative
density - a mineral's
weight compared to an equal volume of water. This can be measured by an
instrument called jolly
balance (there are other, more complicated instruments
too), but
in practice you can get an idea about specific gravity by hefting
minerals in your hands
and comparing which one "feels" heavier.
Mohs' hardness scale. ©collecting-rocks-and-minerals.com
Hardness
Mineral
hardness is one of the most useful mineral characteristics
which, once you get
used to it, is
quite easy to measure. It refers to the mineral's resistance to being
scratched - not its resistance to being broken.
Experienced geologists
use a scraper
which gives them quite a good idea of a mineral's
hardness. But there are easier, and more exact measures for the less
experienced. One way is to use Mohs' mineral hardness
test,
or Mohs'
hardness minerals. You can
also use a home-made mineral hardness kit, where coins
have a hardness of 3, a knife blade has a hardness of 5 and a piece of
glass has hardness of 6.
Mineral cleavage. By play4smee via Flickr.com
Cleavage
Both
cleavage and
fracture refer to a mineral's resistance to be broken.
Cleavage refers to a mineral breaking
along weakness plains. Cleavage
surfaces, while not perfectly smooth, are plain and not uneven.
Cleavage can be perfect, distinct, indistinct, or none.
Mineral fracture. By Orbital Joe via Flickr.com
Fracture
Fracture
is seen when you break a mineral and the broken surface is uneven.
While
most minerals will both fracture and cleave, fracturing is more common.
Fracture can be splintery, hackly, conchoidal or uneven. You can test
cleavage and fracture using a proper geological hammer
or different
chisels.
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