Laboratory Formation of Taranakite — Liu, Sherman, and Swindale 
503 
synthesized taranakite prepared by Haseman 
et aL (1950) and considered that the taranakite 
was hexagonal and uniaxial negative. In the 
original report Haseman et ah described their 
synthesized product as pseudohexagonal and 
biaxial negative. It seems that taranakite might 
exist dimorphously, with 2V values ranging 
from 0 to about 20 degrees. 
Infrared analyses of the phospho-reaction 
product and the synthesized taranakite were car- 
ried out. The phospho-reaction product from 
the Akaka soil was formed with 0.4 molar 
potassium phosphate, at pH 2, and 5 g of wet 
soil. The reacting system was left to stand for 
200 days before the reaction product was col- 
lected. Purification of the phospho-reaction 
products was conducted by repeated reprecipi- 
tation with potassium hydroxide in phosphoric 
acid solution. The samples were ground, mixed 
with potassium bromide, and pressed into discs, 
and infrared spectra were obtained using a 
Beckman infrared spectrophotometer. 
The infrared spectra of the phospho-reaction 
product produced from Akaka soil, and of the 
synthesized taranakite, in pressed KBr discs, 
were in good correspondence with each other. 
The patterns obtained are shown in Figure 1. 
Absorption peaks near 3400 cm -1 showed the 
presence of water of crystallization. Corbridge 
and Lowe (1954) reported that all hydrated 
salts absorb in the 33QO-cm _1 and l640-cm _1 
regions, which presumably correspond to O-H 
stretching and O-H bending, respectively. Com- 
plex phosphate absorption bands between 1200 
cm -1 and 870 cm -1 and P-OH linkages near 
2500 cm -1 indicated the presence of P0 4 3- 
and acidic phosphate ions, respectively (Cor- 
bridge, 1956). These values are very close to 
the infrared absorption spectrum for taranakite 
obtained by Arlidge et al. (1963). 
Differential thermograms of the phospho- 
reaction product and the synthesized taranakite 
samples were obtained. The differential thermal 
setup is the same as the one described by LJehara 
and Sherman (1956). 
The differential thermal curves show that 
both the phospho-reaction product produced 
from the Akaka soil and the synthesized tarana- 
kite undergo endothermic reactions at about 
230°C and exothermic reactions between 500° 
WAVENUMBER GM." 1 
8 000 5000 2000 1800 1096 800 700 
PHOSRH0- REACTION PRODUCT 
Fig. 1. Infrared absorption spectra of soil-phos- 
phate reaction product and pure synthesized tarana- 
kite. 
and 600 °C. These differential thermal curves, 
which are shown in Figure 2, indicate that the 
phospho-reaction products from Akaka soil and 
the synthesized taranakite both lose their water 
of crystallization in one stage, as evidenced by 
the endotherm at 230 C. Arlidge et al. (1963) 
found similar peaks from samples supplied by 
the Tennessee Valley Authority, but natural 
taranakite from Pig Hole Cave and a synthetic 
taranakite lost their water of crystallization in 
two stages. This variation is thought to be 
associated with variations in degree of crystal- 
linity of particle size. The exothermic peak be- 
tween 500°C and 600 °C probably represents 
the recrystallization of the mineral after it has 
been dehydrated, as suggested by Murray and 
Dietrich (1956). The differential thermal gravi- 
metric curves for taranakite obtained by Ar- 
lidge et al. (1963) revealed that there is no 
weight change during the process of exothermic 
reaction, indicating the possibility of recrystal- 
lization. 
The fact that all the taranakite samples 
studied in this experiment are amorphous to 
X-rays when they are heated above 130°C 
shows that the recrystallized products from 
dehydrated taranakite are too small or too 
poorly ordered to be identified by X-ray 
diffraction. 
The Effect of Time on Crystallite Size of the 
Phospho-reaction Product Produced from the 
Akaka Soil 
The relationship, nk = 2dsin$, deduced by 
Bragg , describes the conditions under which 
electromagnetic waves reflected from a set of 
planes in a crystal will be in phase with each 
other. The relationship requires that the planes 
be semi-infinite in the two dimensions perpen- 
