KISH

GEOCHEMICAL STUDIES OF PUMICE

215

Table 3. Index of Refraction Measurements of Florida Pumice Artifacts.

Sample Location Refractive Predicted Predicted Measured Residual °
Index ! SiO, * RIL. 3 SiO2 4
Southern Florida
MDC 1.567.6b Miami Circle 1.504 71.8 1.509 71.1 0.7
MDC 1.166.4 Miami Circle 1.498 73.5 1.493 75.1 -1.5
MDC 1.222.1la Miami Circle 1.505 71.5 1.557 62.5 9.0
MDC 1.472.4 Miami Circle 1.499 73.2 1.493 75.8 -2.5
MDC 1.893.1 Miami Circle 1.501 72.7 1.490 76.0 -3.3
HMSF 896 Brickell Point 1.499 73.2 1.488 75.2 -2.0
FBAR 75.62.10.1 Higgs Site 1.489 76.2 1.489 77.0 -0.8
FBAR 72.20.534.1 IndianKey 1.499 73.2 1.49] 76.0 -2.7
FLMNH A16262a Fort Center 1.496 74.1 1.487 76.7 -2.6
FLMNH 98576 Bear Lake | 1.498 73.5 1.497 74.9 -1.4
HMSF 582.1 Brickell Point 1.496 74.1 1.501 72.2 1.9
HMSF 1018.18 Granada 1.500 72.9 1.505 71.0 2.0
HMSF 2942.1 Honey Hill —-1.503 72.1 1.499 72.8 -0.8
HMSF 427.5 Custom House 1.619 46.9 1.639 47.0 -0.1
FBAR 74.2.10.8 Stock Island 1.500 72.9 1.491 75.1 -2.2
FBAR 00.14.47.1 Deering Estate 1.497 73.8 1.491 75.0 -[.1
FBAR 76.209.1.1 Shark Butchery 1.502 72.4 1.487 75.6 3.2
FBAR 99.65.7.1 Whitebelt 1 1.497 73.8 1.475 62.4 11.4
HMSF 1874.1b Sutton Site 1.501 72.7 1.554 60.3 12.3
Northwestern Florida
EGLIN 056 Wynnhaven = 1.514 69.0 1.549 64.6 4.4
EGLIN 198 Wynnhaven =:1.498 73.5 1.597 51.6 21.9
EGLIN 742 Wynnhaven 1.498 73.5 1.519 71.7 L81

1. Index of refraction measured at a wavelength of 589 nm using an Edmund Optics narrow bandpass interference filter and Cargille Laboratories
refractive index liquids (A-X series) at a temperature of 23°C. The refractive index of individual samples is reported to the nearest 0.001.
Samples with an odd number in the thousandth place (e.g. 1.501) are based upon bracketing values between higher and lower refractive index
liquids.

2. SiO, weight percent values based on the predicted median value derived from SiO," refractive index curves reported by Fisher and Schmincke
(1984).

3. Theoretical value for an anhydrous glass with the same major element composition as the sample (Table 4). Theoretical refractive index
values are based upon the empirically derived coefficients reported by Church and Johnson (1980).

4. Whole rock SiO, weight percent (Table 4), recalculated to an anhydrous whole rock equivalent.

5. Residual values represent the difference between the predicted SiO, versus the chemically measured SiO, content of a sample (in weight
percent).

fingerprinting and to evaluate the possibility that these samples
may be chemically altered.

Predicted SiO, concentrations, based on refractive index, range
from 69.7-76.2 weight percent SiO, and are within the predicted
index of refraction range for rhyolite (Church and Johnson
1980). The SiO, values derived from refraction measurements
(Table 3) are very close to the measured SiO, values for the
same samples. This indicates that the glass within the pumice
has not been significantly altered by hydration. Three samples

Results

The glass from light-colored pumice has relatively low
indices of refraction, ranging from 1.489-1.505 (Table 3).