Take this for granite...

Another easy one.

A granite from my recent fieldtrip
to Serbia.

Black = biotite
Translucent grey = quartz
White = albite
Pink = orthoclase

The largish orthoclase in the middle
right side is about 0.4 cm long.

Got that? 

Oolitic Chert

Aha! This is the sample Hazel found on the Aliakmon,
and it's a beauty!

The matrix is Fe-rich silica, now chert.

Each of the roundish ooliths are about 0.5 cm, and
their centers consist of nuclei of various sorts.
Some are greenish and look like rock fragments, others
whitish and perhaps shells. Or even shark teeth fragments?This one needs a good
microscopic examination.

Ooliths are merely little mudballs rolled around by low,
steady waves. Most form in carbonate (coral) sands in shallow waters and then become oolitic limestone.,
But these are indeed siliceous, causing a great deal of sparking when being sliced with the rock saw. This implies a much
greater depth. I'll read up on these and get back
to you.

The width of the sample shown is about 2 cm.

Travertine

Travertine is deposited by water
and can make up stalagmites
and such. Just another kind of
calcium carbonate, but in this
sample, some lovely crystals
of calcite have formed.

The sample is about 3 cm on each
side. 

More forms of Quartz

This is part of the wall of an open geode.

Everything you see is some sort of silica.

All the crystaline silica is good old quartz, smoky quartz, which looks white at the fim itself. Further in, is a rim of greyisn smooth
chalcedony.

The rim itself is probably a mix of chalcedony
with microcrystalline quartz, and a tad of
opal mixed in for good measure. Love the
way it grew in cloudlike form as it filled in
the vug in the lava. 

Metalliferous Sediment aka Jasper

This is an easy one.

The red mateterial is iron-rich silica "mud." You can
note white veins and irregular blebs, also
a silica, chalcedony. The yellow-greenish-grey
patches around the margins are altered remnants
of sulphides.

The entire fragment is about 5 cm. wide.