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may notice the end-notes don't necessarily start at "1". The
following article is an excerpt from a back issue of our newsletter.
Qualitative Analysis of a Jade-Like Rock
by C. Thorsten
obtained a green, mottled rock which had come from a beach in the state
Washington. The collector who had originally found it stated that in
of walking up and down that beach, he'd found no other rocks like it.
very little familiarity with northwestern Washington and being
to recognize its mineral assemblages simply by looking at them, the
decided to resort to some fairly simple qualitative tests.
Figure 1 shows a slab cut from the rock.
Figure 1. A slab cut from the beach rock.
greenish, almost teal
1. Visual and Mechanical Properties:
scratch tests, concentrating on the greenish mineral grains,
suggested a hardness of 6 to 7; this measure was
to obtain precisely, even when studying the surface of the specimen
magnifier. There was some doubt whether a hardness sample really did make a scratch, or
was simply a polished streak that looked
like a scratch. The
able to scratch orthoclase (H=6) definitely, but only after repeated
Orthoclase, on the other hand, was not able to scratch the unidentified
stone at all. Finally, the stone was completely unable to scratch
quartz (H=7). Therefore, it seeemed reasonable to assign H=6.5 to
The unidentified stone had a high overall
toughness (resistance to crushing), as evidenced by its
make up any
given rock, but a rock is not always made of a single mineral;
different minerals are in grains too small to tell apart. In the case
unidentified beach rock, the zones of green and of white seemed to be
different composition from the darker (brown) regions, which appeared to be
products of the green / white mineral or minerals. These dark, mostly brown regions seemed to
along grain interstices and old micro-fractures where water could have
its effect through the ages.
examined at 10x and 30x. It had a greasy or waxy luster; the overall
was reminiscent of something from the serpentine or chlorite groups. A
needle was used under the microscope in an attempt to scratch some of
material, which proved to be very soft: estimated hardness perhaps 2,
than 3. It smeared in very much the same manner as talc or
alteration minerals that one might find in certain marble or skarn
harder, around 6.5 as stated before. Inspection at 10x and 30x
was not at all amorphous; rather, it seemed to be a fairly
silicate made of interlocking crystal grains. Though the material
exhibit cleavage, massive-form minerals often behave this way.
Cleavage, therefore, is not an especially useful property unless one is
dealing with definite
The green mineral did exhibit vaguely splintery fracture
habit which could be
clearly with and even without magnification. This habit was
entirely different from anything the author had ever observed in
chalcedony (i.e., chert, jasper, or agate). Figure 2 doesn't
adequately capture the play of light that gave away the
crystal grains, nor does it show off the splintery fracture, but these
visible in real life.
Figure 2. The green mineral at 10x magnification
2. Fusibility: A chip consisting mostly of the greenish
only along thin edges in the propane torch flame (somewhere between
1900°C at the hottest portion). These edges melted fairly quickly,
continued heating did not melt the thicker portions at all. The flame
bright sodium-yellow with a fine but persistent border of red to
or possibly Sr). The mineral's green color disappeared, leaving an
pale yellow color.
3. Closed Tube Test: A short piece of 5 mm borosilicate glass
off at one end by heating, served as the closed tube. The
mineral sample did give off some water upon prolonged heating. No other
sublimates were observed.
4. Solubility: A fragment placed in concentrated HCl did
not seem to
dissolve at all, but the solution turned from colorless to strong
added to this yellow solution, and a considerable amount of rust-brown
precipitate quickly formed. The yellow color disappeared. When the
was taken out of the liquid and washed, it was evident that the brown,
serpentinaceous mineral had dissolved in the HCl but the green mineral
5. Bead Tests: Perhaps to the relief of some readers, but
disappointment of others who were hoping the CR Scientific Newsletter's
apparent monomania for element 25 might never end, the bead tests did
suggest the presence of manganese in the sample. Furthermore, there
differences this time between the "hot" and "cold" states
of the beads.
Following are the observed results:
Borax - R.F.- Yellow (hot); Nearly Colorless with a faint aqua tinge
Borax - O.F. - Bright Yellow (hot); Colorless (cold)
Salt of Phosphorus - R.F. - Colorless (hot); Colorless (cold)
Salt of Phosphorus - O.F. - Bright Yellow (hot); Colorless (cold)
Sodium Carbonate - R.F. - Muddy Yellow-Brown (hot); Pale Green (cold)
Sodium Carbonate - O.F. - Muddy Yellow Brown (hot); Dirty Yellow (cold)
6. Chromate Flux: Powdered sample was fused on the carbon
chromate flux (1 part KHSO4, 1 part K2CrO4,
parts sulfur; as per Smith, 1953). The coating near the assay was pale
same color, hot or cold.
7. Iodide Flux: (1 part KHSO4, 1 part KI, 2
parts sulfur; as
per Smith, 1953) The coating near the assay was dense white, fading to
white at some distance from the center. This outer coating was volatile
reducing flame, but the inner coating was very stable. There were some
definite yellow spots also noted. The coating looked the same, hot or
8. Aqueous Chemical Tests
To prepare the
sample for dissolving, it was mixed with an equal volume of sodium
and fused on the carbon block. The fused mass was allowed to cool for
20-30 minutes and then crushed into powder.
powder was placed in a micro
beaker and covered with dilute HCl. Profuse bubbling occurred. A
and highly insoluble residue now floated in the liquid, eventually
the bottom. The solution remained colorless, and there were still
lumps at the bottom.
In order to
dissolve the remaining sample, concentrated (37%) HCl was carefully
the micro beaker. The bubbling became severe, and the solution quickly
bright yellow with the slightest influence of green. The color remained
material was allowed to settle. The yellow solution was siphoned off
with a dropper for further tests.
A drop of
this solution was added to a spot plate containing potassium iodide.
This caused it to turn a deep and pure shade of yellow (as opposed to
hint of greenish, which the HCl solution had before this). Adding
to this destroyed the yellow color completely.
About 1/2 mL
of the same solution (from 8D) was placed in a small test tube. The
strong sodium hydroxide caused a cloudy, white precipitate to
Excess NaOH failed to make this precipitate redissolve, as far as could
seen. A separate aliquot of solution was tested with aqueous ammonia
instead of NaOH; this also caused a white precipitate which turned
on standing. Excess ammonia did not dissolve the precipitate.
aliquot of solution from 8D was placed in a clean test tube and brought
using NaOH, to a pH just below neutral. The addition of sodium
phosphate (salt of phosphorus) caused a cloudy white precipitate,
presumably MgNH4PO4 • 6H2O.
A drop of the
solution from 8D was added to a spot plate well containing potassium
chromate. The solution immediately turned bright orange and cloudy;
HCl made the cloudiness disappear, but the orange color persisted.
pH back up to around 3-4 (by adding NaOH) made the orange compound
About 1/2 mL
of the solution from 8D was placed in another small test tube. Adding ammonium
sulfide solution caused a cloudy to almost
precipitate that was dark gray to black. It is not certain whether this
compound or two; around the edges the material was white, suggesting
hydroxide mixed with a sulfide ((NH4)2S can
both if the right ions are present). Boiling the suspended precipitate
it to turn rust-brown in the final stages of heating. When it was cool,
residue was taken up in a few drops of dilute HCl. Addition of sodium
hexacyanoferrate (II) caused the color to turn deep green to
(this was not the typical deep blue of Prussian Blue; it's possible the
was caused by the the similar iron hexacyanoferrate compound
Green / Berlin Green, which could form under the right conditions).
mL of the solution from 8D was placed in a clean test tube and brought
below pH 7 with NaOH (the point at which the hydroxide precipitate
with difficulty). Saturated aqueous oxalic acid was then added
solution boiled for several minutes. No precipitate formed at first,
next day there was a white, crystalline precipitate at the bottom. This
washed several times in distilled water, placed in a crucible and
conc. HNO3, and evaporated to dryness (fume hood!!) to
oxalate. The residue was then taken up in HCl and made alkaline with
ammonia. There was no precipitate noted, suggesting a lack of Th, Sc,
rare-earth elements but not ruling out Ca, Ba, or Sr (as per Chapter
Procedure 4 in Smith, 1953)
mL of the solution from 8D was tested with metallic zinc. No
change was observed, even after boiling. This suggests the absence of
Just to be
sure of no Mn, Co, or Ni, an aliquot of solution from 8D was made
ammonia. In the presence of NH4Cl (as would be the case when
neutralizing HCl with ammonia solution), these three will not come out
solution until boiled with H2O2 (Smith,
This treatment caused no observable changes in the test solution.
Conclusions and Discussion
rock's physical properties, taken together with the chemical test results, suggest a variety of jade; the elements
reasonable certainty are Si, Fe, Na, Ca, and Mg. The following is a
list of the
steps which gave the best evidence:
Iron......step 8I and step 5, especially the sodium
There might have been interfering ions which prevented the green color
coming out in the R.F. beads of borax and salt of phosphorus-- possibly
hindering the reduction of Fe+3 to Fe+2.
Sodium....... the yellow flame test
Calcium......step 8J and the red-orange flame test
Magnesium......steps 8F and 8G
suggested in the tests was Lead, Pb (steps 7, 8E, 8H). The fact that NaOH
yellow precipitate in the KI test to disappear is actually not
first of all, PbI2 is soluble in alkali (check any suitable
reference, such as the CRC Handbook of Chemistry and Physics);
lead forms an amphoteric hydroxide, meaning that it will dissolve in
NaOH to form a colorless, complex ion. Sorum (1953) indicates this is
with the formula Pb(OH)4-2. As for the formation
orange precipitate rather than a yellow one in the chromate test (8H),
that lead chromate can be either yellow or orange depending on what
formed it (example: crocoite). The colors observed in the borax and
phosphorus bead tests (step 5) don't at all contradict the possibility
in the sample, either.
might have been useful? There are quite a few: specific gravity,
quite a few more chemical tests; the possibilities are limited only by
equipment the experimenter has available. Note that we didn't even test
flocculent residue from step 2 for W, Ta, or Nb, for example; nor did
attempt to precipitate the suspected Pb+2 ions using cold
one would do in a typical qualitative analysis scheme 6. The presence of Mo, V, and a few
could have been sought as well. Once again, the
author performed enough
to give at least a plausible idea of the subject's identity: a variety
probably an amphibole and most likely nephrite 7,
a mineral whose green color is caused by
ferrous iron, and which may contain traces of lead and other elements
present either as part of the primary mineral or as constituents of
minerals present in grains too small to pick out (but which found their
into the crushed sample and therefore the chemical tests).
this has been
an informative journey for our readers... it was certainly enlightening
writer, who originally thought the rock was green jasper!
any Pb present
would've remained in solution, thanks to the strong HCl added to the
fusion (which also released heat). To precipitate lead as the chloride,
requires cold, dilute HCl. Back
(actinolite) doesn't contain sodium in its formula, we've already
seawater possibility. Alternatively, our mineral could be one of the
amphiboles or pyroxenes similar in composition to actinolite but off by
sodium atom here and there... the number of different silicate minerals
can possibly contain Fe, Ca, Mg, and Na is impressive.
Back to article
Brush, George, and Penfield, Samuel. Determinative Mineralogy and
Analysis, 16th ed. New York: John Wiley & Sons, 1926.
Smith, Orsino C. Identification and Qualitative Analysis of Minerals,
2nd ed. Princeton, New Jersey: D. Van Nostrand Co., 1953.
Sorum, C.H. Introduction to Semimicro Qualitative Analysis, 2nd
York: Prentice-Hall, 1953.
While the information in this
thought to be accurate to the best of the authors' current knowledge,
it is not
guaranteed to be free of errors or to be suitable for any particular
procedures and experiments outlined within can be dangerous or
even fatal if carried out improperly. If you choose to attempt
any of them,
you proceed entirely at your own risk.
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