Journal of the Royal Society of Western Australia, 87(4), December 2004 
Figure 10. SEM photomicrographs of diatomite. A. Diatomite from a wetland basin in the Bassendean Dunes, east of Yanchep, showing 
typical view of diatom frustules in various stages of fragmentation (arrow 1), sponge spicule (arrow 2), and scattered kaolinite particles 
(arrow 3). B. Close-up showing the stages of fragmentation of diatom frustules: semi-complete diatom valve (arrow 1), 30 pm in size, 
fragmented valves (arrow 2) and (arrow 3), 15 pm in size, and 3-5 pm in size, respectively, leading finally to small fragments (arrow 4), 
< 1 pm in size. C. Close-up of diatomite from Lake Gnangara, showing diatoms in generally fragmented state; fragments show clear 
wall features such as sieve structure; particle sizes are mainly 1-5 pm; examples of diatom'fragments < 1 pm in size are circled; the 
sample contains scattered quartz silt (arrow). D. Close-up of diatomite from Lake Gnangara showing diatom frustules in various stages 
of fragmentation from 3 pm in size, and showing wall structure (arrows), to 1—2 pm in size, and showing remnants of wall structure, to 
< 1 pm in size and structureless; the particles in this SEM view are adhering to a quartz silt particle (partial margin outlined). 
deposits (Fig. 4B-G). Commonly, the intraclasts are 
embedded in a fine-grained diatomite matrix. 
Kaolinitic mud 
Kaolinitic mud deposits vary from white, orange, dark 
brown, and dark grey to black, and are homogeneous to 
root-structured. Locally, the mud beds exhibit polygonal 
cracks. Texturally, the mud deposits are composed of 
mostly clay-sized and silt-sized particles with scattered 
(< 5%) quartz sand. In sumpland and former sumpland 
basins, there also is occurrence within the kaolinitic mud 
of fragmented diatoms, sponge spicules and phytoliths. 
Compositionally, while these deposits are mainly 
kaolinite, locally, there may be some montmorillonite and 
fine-grained white micas such as muscovite or 
paragonite. Admixed with kaolinitic mud deposits also 
are small amounts of quartz and feldspar silt. 
Quartz sand 
Quartz sand is white, or light to dark grey deposit 
that is structurally homogeneous, bioturbated or root- 
structured, locally wispy laminated, and locally vesicular 
(Fig. 5E-F). In some areas, where freshwater Crustacea 
are common, the sand is burrow-structured, with vertical 
burrows, up to several centimetres in diameter. 
Texturally, quartz sand is mostly well sorted, medium¬ 
grained and well rounded, though it may vary to poorly- 
sorted, mixed coarse, medium and fine in grainsize. Its 
composition is dominantly quartz, with minor feldspar, 
and minor amounts of heavy minerals. 
Quartz silt 
Quartz silt is cream to light grey, and structurally 
homogeneous to root-structured. It consists of silt-sized 
and some clay-sized silica particles, with scattered (< 5%) 
quartz sand. In sumpland and former sumpland basins, 
there is occurrence of fragmented diatoms, sponge 
spicules and phytoliths in the sediment. Deposits of 
quartz silt form only thin units in isolated wetlands. 
Mixtures of sediments 
While the sediments described above occur as end- 
member types, many wetland deposits are mixtures of 
these. The most important gradational series are between 
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