INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 26: 691–706 (2006) Published online 21 October 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1269 MICROCLIMATE PROCESSES CHARACTERIZATION OF THE GIANT GEODE OF PULP ´ I (ALMER ´ IA, SPAIN): TECHNICAL CRITERIA FOR CONSERVATION A. FERN ´ ANDEZ-CORT ´ ES,* J. M. CALAFORRA, F. S ´ ANCHEZ-MARTOS and J. GISBERT Water Resources and Environmental Geology Research Group, Department of Hydrogeology and Analytical Chemistry, University of Almer´ ıa, 04120 Almer´ ıa, Spain Received 7 April 2005 Revised 1 July 2005 Accepted 15 August 2005 ABSTRACT The giant Geode of Pulp´ ı (Almer´ ıa, Spain) can be considered as one of the most significant recent mineralogical discoveries in terms of geological heritage. Any tourist exploitation of this mining environment should be sustainable, and the first step is to determine the feasibility of opening the interior of the geode to visitors. To achieve this objective it was necessary to characterize the variation of physical parameters of the air and rock (gypsum crystals) during monitored visits, similar to the hypothetical visits that would occur if the geode were opened to the public. The main environmental impact of a continuous presence of people inside the geode is condensation on the surface of the gypsum crystals as a result of increased temperature and water vapor caused by respiration. The phenomenon of condensation on the gypsum crystals begins to occur with visits of two or three people for longer than 10 min. Condensation on the crystal surface brought about by this human presence could lead to the corrosion of the crystals. The total recovery time required after a visit of this type to resume the initial natural thermal and humidity conditions was 27 h. The results obtained from the environmental monitoring of the geode suggest that it is not feasible to allow visits inside it because of the mechanical impact of the visitors on the crystals and of the risk of condensation of water vapor. Copyright  2005 Royal Meteorological Society. KEY WORDS: geode; geological heritage; cave microclimate; cave management; gypsum 1. INTRODUCTION The Geode of Pulp´ ı (SE Spain) is a geological phenomenon unique in the world because of its size and the perfect shape of the large crystals it contains (Calaforra and Garc´ ıa-Guinea, 2000; Garc´ ıa-Guinea and Calaforra, 2001a). These crystals have high transparency and contain minor solid inclusions. Its discovery in 1999 by mineral collectors was widely publicized in the world media and it made news in some scientific journals like Science (Vol. 286, 2000, p2120). It was found inside an old iron-and-lead mine, 50 m deep (Figure 1) in Triassic dolomites that form part of the Betic Cordillera. The volume of the void of the Geode of Pulp´ ı is 10.7 m 3 ; it is 8 m long, 1.8 m wide and 1.7 m high, and the average size of the gypsum crystals is 0.5 × 0.4 × 0.3 m, with some crystals of 2 m in length. Mineralogenesis of the geode can be summarized in four stages (Garc´ ıa-Guinea et al., 2002): (1) karstification of Triassic dolomites under conditions of pronounced acidification and in the presence of hydrothermal fluids rich in hydrogen sulfide; (2) deposition of fine needles of celestine in the walls of the void generated (SrSO4); (3) influence of the freshwater–saltwater mixing zone in the carbonate aquifer and mixing with hydrothermal fluids (H 2 S); and (4) gradual cooling with slow growth of gypsum crystals sealing in the fine celestine needles. * Correspondence to: A. Fern´ andez-Cort´ es, Water Resources and Environmental Geology Research Group, Department of Hydrogeology and Analytical Chemistry, University of Almer´ ıa, 04120 Almer´ ıa, Spain; e-mail: acortes@ual.es Copyright  2005 Royal Meteorological Society