Geoscience Reference
In-Depth Information
Subject
Method summary*
Observation
Dickson's method
1,2
is the most useful scheme for
Carbonate
Calcite stains pink to red. Ferroan
minerals
carbonates
which in one operation differentiates
calcite stains purple (mauve) to dark
between nonferroan and ferroan phases in both
blue. Dolomite is unstained. Ferroan
calcites and dolomites: etch for 10 s in 1.5%
dolomite stains very light blue
HCl. 30 s immersion in 1:1 g Alizarin Red S
(turquoise). Aragonite stains pink to red.
+ 0.9 g potassium ferricyanide in 100 ml 0.5%
HCl. 10 s immersion in 0.2 g Alizarin Red S in
100 ml 1.5% HCl, wash in water.
Dolomite
is often recognized by its failure to stain
Dolomite stains deep orange red.
when using Dickson's method. For specific dolomite
Magnesite stains orange to red. High
detection use a method such as this one described
magnesium calcite stains orange. Calcite
by Tucker
3
: 5 min immersion in a boiling solution
and aragonite remain unstained.
of Titan Yellow solution (0.2 g Titan Yellow
dissolved in 25 ml methanol by heating, top up to
25 ml with more methanol and then add 15 ml of
30% sodium hydroxide solution).
Haines
4
method detects
brucite
and dolomite: etch
Brucite stains purple and calcite pink,
for 3-5 s in 5% HCl. Apply reagent (0.2% Alizarin
while dolomite remains unstained.
Red S in 0.2% HCl) drop by drop until strong pink
colour develops on calcite, wash in water.
Fiegl
5
method specifically for
aragonite
:
Aragonite is stained black while calcite
10 min immersion in Fiegl's solution at 20°C.
and dolomite remain unstained.
Fiegl's solution is made by adding 1g silver sulfate
to a boiling solution of 11.8 g manganese sulfate
in 100 ml of water. Cool and filter the suspension;
add 2 drops 10% sodium hydroxide solution. Filter
into a dark storage bottle after 2 h.
Houghton
6
method for staining plagioclase and
Feldspars
Alkali feldspars stain yellow. Pure na-
alkali feldspars: etch over hydrofluoric acid vapour
albite remains unstained; other
(55% HF solution) for 25-35 s. 45 s immersion in
plagioclases stain pale to deep pink in
saturated sodium cobaltnitrate solution. Gently
proportion to the amount of calcium in
wash in water, blot dry, and then 2 s immersion in
the molecule: albite/oligoclase will stain
5% barium chloride solution. Water wash and place
lighter than a more calcic plagioclase.
several drops of potassium rhodizonate solution on
Quartz remains unstained.
surface (0.01 g K-rhodizonate in 30 ml distilled
water). Leave until plagioclase grains become
pink and wash in water.
Shand
7
method for feldspathoids: spread a thin layer
Feldspathoids
Nepheline, sodalite, and alacime stain
of 85% (syrupy) phosphoric acid over specimen with
deep blue. Melilite stains pale blue.
glass rod. Wait 3 min and wash gently in water.
Leucite remains unstained. Zeolites also
Immerse in 0.25% methylene blue solution for 1 min,
stain blue.
wash in water.
