220

THE FLORIDA ANTHROPOLOGIST

2006 VOL. 59(3-4)

 

6.0

KO [wt%]
oo > on
oS oS So

N
SoS

\
\

1.0

0.0

ST

  
  

O BL

QO) HH
Medium-K oR

MC O

Low ~K

 

40.0 50.0

60.0

70.0 80.0

SiO, [wt%]

Figure 6. K,O versus silica classification diagram for Florida pumice artifacts. The symbol notation is the same as that used
in Figure 8. The explanation for the letter code for medium-K samples is location on Figure 1. Classification diagram

modified from Peccerillo and Taylor (1976).

rhyolites.” Two samples, one from the Miami Circle site
(1.222.11a) and one from the Sutton Site (1874.1b) have
andesitic compositions. A single sample from southern Florida,
Custom House (HMSF 427.5), has a mafic, near-alkaline,
basaltic composition. Selected pumice samples from the
Wynnhaven Beach site in northwestern Florida appear to have
amuch more heterogeneous compositional range, including low
silica rhyolite, dacite, and basaltic trachyandesite (Figure 5).
The TAS classification for these sample is substantiated using
the normative mineral classification of Irvine and Baragar
(1971) — all samples classified as rhyolites using the TAS
diagram have less than 10 percent normative mafic minerals
and less than 20 percent normative anorthoite (Table 5) and a
high differentiation index (the sum of all “felsic” normative
mineral), which ranges above 90 percent for most samples.
The chemical compositional characteristics of pumice
samples can be refined using the KO versus SiO, classification
of Peccerrillo and Taylor (1976). All rhyolitic samples from
the Miami Circle site have a high-K composition (Figure 6).
The rhvolite samples form the Granada (8DA1 1). Honey Hill

(8DA411), and Bear Lake 1 (8MO33) sites have a medium-K
composition. The andesite samples from the Miami Circle and
Sutton sites also have medium-K compositions. Mafic samples
have moderate to distinctly alkaline signatures using TAS
classification . The Custom House basalt scoria (HMSF 427.5)
has normative olivine (Table 5) and a very high concentration
of TiO, (4.45 wt. %) and P,O, (1.72 wt. %). These values are
exceptionally high, so they were checked with additional
replicate analyses (see footnote in Table 4). Somewhat lower
concentrations of TiO, (2.36 wt. %) and P,O, (1.14 wt. %) are
present in the pumaceous basalt (EGLIN 198) from the
Wynnhaven Beach site along the northwestern Gulf Coast. The
elevated TiO, and P,O, concentrations observed in these
samples are normally associated with alkaline mafic rocks. The
grouping of pumice material that is present on TAS and SiO,
versus K,O diagrams also is reflected in distinct grouping of the
same samples on rare earth element diagrams, which is dis-
cussed in a later section. The chemical classification names for
all the samples are listed in Table 6. High-silica, high-K,
thyolitic pumice is the most widely distributed type of material.