| In these, the spicular aspect grades abruptly inward into dense cryptocrystalline silica, which forms the bulk of the specimen. |
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| They are largely silicified replacements of the once opaline skeletons, but details of their spicular and skeletal relationships are moderately well preserved. |
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| Subsequent microscopic study of the outer layer shows that, in a few specimens, patches of the microcrystalline material grade laterally into vestigial spicular fabric. |
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| However, in specimens in which the secondary rays are well developed, the spicular structure becomes complicated and the primary six-rayed spicule is difficult to discern. |
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| The expanded mesangial areas are silver negative, and a spicular arrangement similar to that described in amyloidosis may be seen. |
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