Leçon :
Histoire et définition : L'altération ou dégradation du calcaire est due aux substances chimiques comme le dioxyde de soufre et les oxydes d'azote, issus de la pollution atmosphérique, ils réagissent avec la pierre et la dissolvent. Il se forme parfois une croûte de gypse (minéral issu d'un sulfate hydraté de calcium) dure et foncée à l'extérieur, laissant apparaître une pierre tendre et friable en dessous. La pluie, le vent et la neige peuvent également causer des problèmes, les cycles de gel-dégel hivernaux provoquant l'apparition de fissures. Mais le processus d'érosion du calcaire reste énigmatique, on observe souvent un bloc de calcaire se creuser, tandis que les blocs environnants demeurent intacts. On ignore ce qui rend un bloc plus vulnérable qu'un autre.
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With Flo, we share a great passion for geocaching: EarthCaches 🥰. We are intense rock hunters! 🪨😄 You could even say it’s a real crush 🤢. Our second geocaching passion is GeoArt 🤩. So we pushed ourselves a bit and decided to mix the two. A big headache to set up 😵, but in the end, totally doable.
Questions : Locate the blue areas in the photo above and answer the following:
1 - Which mineral forms a hard, dark crust on the outside ?
2 - Based on your observation, what is the color of this alteration ?
3 - What type of alteration is this ?
4 - Take a photo in front of the wall with your geocaching username visible and make a 🖖 sign with your hand.
arthCache Rules: "Log this "Found it" cache and send me your suggested answers either via my profile or via email, and I will contact you if there is a problem."
Lesson :
History and definition : The alteration or degradation of limestone is due to chemical substances such as sulfur dioxide and nitrogen oxides, produced by air pollution. These substances react with the stone and dissolve it. Sometimes, a hard, dark crust of gypsum (a mineral derived from hydrated calcium sulfate) forms on the outside, revealing a soft, crumbly stone underneath. Rain, wind, and snow can also cause problems, with winter freeze-thaw cycles leading to the appearance of cracks. However, the process of limestone erosion remains enigmatic. Often, a block of limestone is observed to be hollowed out while the surrounding blocks remain intact. It is unknown what makes one block more vulnerable than another.
Happy Géocaching everyone 😎