Chalcedony refers to a microcrystalline variety of silica (SiO2) consisting mainly of quartz, whose deposition at low temperatures (20-200°C) in successive concretionary layers produces mamillary or botryoidal forms.
Agate, jasper, and flint are types of chalcedony familiar to collectors.
Opal, on the other hand, contains less organized, non-crystalline (known as “amorphous”) siliceous material and is not considered chalcedony.
Although chalcedony is ubiquitous in a wide range of geological environments, from marine sediments to hydrothermal veins, good geode and colored specimens are rare worldwide.
The jewel in the crown of the O. Fumery collection, acquired in early 2025, was, in our opinion, a spectacular set of more than twenty chalcedony geodes from the Pays de Caux on the Normandy coast.
Passionately assembled over more than 40 years of research and acquisitions by C. Presa and O. Fumery, this collection is undoubtedly the most complete set of chalcedony from this iconic region assembled in recent decades!
Notable characteristics
Exceptional chromatic diversity
This suite presents a strikingly varied palette of appearances and colors. From milky white to deep red, including rarer colors such as intense black, delicate blue, and orange. Appearances vary from pearly to shiny, with some specimens displaying opalescence and others a subtle translucency.
Diverse morphology
Most specimens occur as characteristic globular clusters with botryoidal surfaces typical of chalcedony. However, some exceptional pieces are finely crystallized in quartz with remarkable luster, sometimes slightly bluish.
Exceptional dimensions
The size of these chalcedonies is remarkable for the region. The largest specimen measures 35 cm, a size rarely achieved in this deposit. These specimens are true objects of study and collection.
Geology and mineralogy-paleontology association
Several geodes have radial symmetry structures on their surface that are typical of cnidarians: with a cushion shape, sometimes accompanied by a short anchoring root, suggesting that all or part of the geodes are in fact masses built from colonies of fossil polyps and bryozoans (in line with the paleoenvironment of the Senonian chalk deposits), whose internal porosity is occupied by siliceous concretions. The diagenetic process probably took place in at least two stages, first involving the dissolution of the carbonate “skeleton” of the colony and then its replacement by silica in a low-permeability environment (hollow geodes instead of solid siliceous nodules).
The occurrence of remarkable mineralizations associated with fossil structures increases the scientific and educational interest of these objects: these geodes carry a geological history, that of the Paris Basin, and illustrate the intimate link between mineralogy, paleontology, and general geology, appealing to the naturalist’s eye of the observer.
Museum recognition
Several specimens from this collection were loaned and displayed as part of the temporary exhibition “Precious Crystals” at the National Museum of Natural History in 1994, demonstrating their scientific and aesthetic value as recognized by the museum community.
Provenance and history
Initial collection by César Présa
This collection was first assembled by César Présa, a prospector and passionate mineral collector from northern France. Through his methodical prospecting and targeted acquisitions, he laid the foundations for this remarkable collection. The finest specimens were gathered by C. Présa.
Development by Olivier Fumery
The collection was then acquired and expanded by Olivier Fumery, a renowned collector from the north (Arques), who continued the work of his predecessor through his own prospecting and acquisitions. Treasurer of the Municipal Sports Office (OMS), Olivier Fumery was also a renowned cycling champion with numerous titles to his credit: entry into the Pool France in 1998, 12th place in the legendary Liège-Bastogne-Liège race, second in the Tour de Bourgogne time trial, and above all – something particularly close to his heart – third place in the Tour de la Haute-Marne time trial, where he beat Philippe Ermenault, the future world champion!
Geological context
The chalcedony of the Pays de Caux was formed in the chalk formations of the Upper Cretaceous period, under specific geochemical conditions that favored the precipitation of silica in the form of chalcedony. These cryptocrystalline minerals result from the intergrowth of two siliceous phases, quartz and moganite, which develop mainly in the cavities and fissures of the chalk, creating these characteristic botryoidal forms.
Geographical distribution and deposits
Chalcedony is quite common among the hollow flint pebbles found on beaches along the Normandy coast, mainly between Ault and Le Havre. It occurs in two main variations: the most common variety is mamelonated, with small hemispherical protuberances in the cavities, and geodes of mini quartz crystals up to several millimeters in size are also found.
The distribution of deposits follows the chalky outcrops of the Cauchois plateau, particularly in fields dotted with flint nodules. These specimens from the Alabaster Coast in Normandy range in color from pale blue/purple to deep orange/brown. It is interesting to note that some of the most beautiful specimens were discovered during earthworks related to the construction of the Paluel nuclear power plant, revealing mineralized pockets that had previously been inaccessible.
Historical use and trade
Chalcedony from the Pays de Caux has long been renowned in the semi-precious stone trade. It was particularly prized for making cabochons exported to England, where they were transformed into jewelry and objets d’art. This lapidary tradition, well documented in commercial archives from the 18th and 19th centuries, attests to the quality of these Norman minerals.
The variety of colors and appearances (pearly, shiny, sometimes opalescent) explains their historical commercial success. The bluish to pinkish, soapy-to-the-touch, mammillary appearance was particularly sought after by lapidaries for the manufacture of decorative objects and jewelry.
Heritage value
This collection is a unique testament to the mineralogical wealth of the Pays de Caux and represents decades of passion and expertise.
These Norman treasures are available exclusively at our booth at MinéraLyon 2025 and on the Mineral Show tab for our VIP members!
