Polished Ammonite Section (Crystallized)
Cleoniceras besairiei • Body fossil; Invertebrate Cephalopod (Ammonoid)
Geological Period
Cretaceous (likely Albian stage)
Estimated Age
100 - 115 million years
Preservation Type
Permineralization with Calcite druse. The internal chambers are partially hollowed and lined with dogtooth/rhombohedral calcite crystals, while others are solid-filled with honey-colored or translucent calcite.
Condition Assessment
Very Good. The ammonite has been professionally sliced and polished to a high luster. The inner septal lines are well-defined, and the crystallization is intact without significant bruising or modern fractures.
Taxonomic Classification
Phylum: Mollusca, Class: Cephalopoda, Order: Ammonitida, Family: Desmoceratidae, Genus: Cleoniceras
Morphological Description
Planispiral, involute shell sliced medially to reveal internal anatomy. Features include numerous camerae (chambers) separated by curving septa. The central protoconch is visible, leading to an increasing whorl breadth. The outer shell demonstrates a smooth, discoidal morphology typical of this genus.
Rock Matrix
Primarily absent due to aesthetic preparation, but the internal filling consists of micritic limestone and secondary calcite mineralization.
Formation & Location
Likely from the Mahajanga Basin of Madagascar (Anisaranay or Jungalina formations).
Size & Dimensions
Approximately 10-15 cm in diameter; a standard medium-to-large size for the Cleoniceras genus specimens found in the Madagascar trade.
Value & Rarity
Estimated Market Value
$80 - $150 USD
Auction Estimate
$60 - $120 USD
Rarity Assessment
Common. Cleoniceras from Madagascar are among the most abundant and commercially available ammonite fossils globally due to mass-scale quarrying.
Scientific Significance
Provides an excellent educational cross-section of cephalopod buoyancy mechanics. While common, these specimens illustrate the complex septal geometry that allowed ammonites to withstand hydrostatic pressure in ancient marine environments.
Preparation Recommendations
Requires no further preparation. Should be kept in low-humidity environments to prevent oxidation of any trace pyrite. Clean only with a soft, dry microfiber cloth to maintain the polished surface.
Notable Features
Outstanding 'druse' crystal pockets within the chambers. The contrast between the grey-white septa and the translucent crystal voids creates a highly aesthetic 'geode' effect within a biological structure.