Laboratory Formation of Taranakite — Liu, Sherman, and Swindale 
505 
form of taranakite is formed when heavy ap- 
plications of fertilizers containing potassium 
phosphate are made to soils of the Hydrol 
Humic and Humic Latosol groups. Current ap- 
plications by sugar cane producers range as high 
as 175 lb of P and 600 lb of K per acre for 
each planting or ratoon crop. Because of the 
heavy rainfall the soils are continually wet. 
Concentrated solutions of potassium phosphate 
have a pH of 4, at which value Al 3 + cations 
and H 2 P0 4 _ anions exist in solution. Many 
times during the decomposition of the applied 
fertilizer, the concentrations will rise high 
enough in the subsurface horizons of the soil 
to enable cryptocrystalline precipitates to form. 
With time these precipitates can be expected 
to grow into larger and better-ordered crystals 
of taranakite. 
CONCLUSIONS 
1. Crystalline taranakite formed when the 
Akaka soil was treated with potassium phos- 
phate solutions ranging from 0.2 to 0.6 molar 
and the pH value of the reacting system ranged 
between 2.3 and 2.9. On heating, the phosphate 
reaction products and a synthesized taranakite 
gave similar dehydration products. 
2. The taranakite was essentially a potassium- 
aluminum-phosphate complex. There was no 
indication of isomorphous substitution of iron 
for aluminum. The molar ratios of K/P0 4 and 
A1/P0 4 for the reaction product were estimated 
to be 0.37 and 0.72, respectively, which agreed 
well with values found for the synthetic min- 
eral. 
3. Optical analysis showed that the tarana- 
kite crystals were colorless and pseudohexagonal 
in form. They were biaxial negative. The re- 
fractive indices were na = 1.504, n(3 = 1.507 
and ny = 1.509, respectively, na — ny = 
0.005. 
4. Structural diagnosis by means of infrared 
spectroscopy of the potassium-aluminum-phos- 
phate complex revealed that water of crystal- 
lization, (P0 4 ) 3_ ions, and P-OH linkages 
were all present. 
5. Differential thermal data showed that 
both the phospho-reaction product and the 
synthesized taranakite underwent an endother- 
mic reaction at about 230°C, and an exothermic 
reaction between 500°C and 600 °C. 
6. It is proposed that potassium and phos- 
phate ions from heavy applications of fertilizer 
may react with aluminum ions in soil solutions 
in the subsoils of Hydrol Humic and Humic 
Latosols to produce cryptocrystalline precipitates 
which, with time, will grow and transform into 
crystalline taranakite. 
REFERENCES 
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