Leçon :
Histoire et définition : Le grès est une roche sédimentaire détritique issue de l’agrégation de grains et consolidé lors de la diagenèse. Les grains qui constituent le grès sont généralement issus de l'érosion de roches préexistantes, qui déterminent en grande partie sa composition, principalement constituée de quartz et feldspath. Selon le degré de cimentation et sa composition, il peut former une roche très friable ou cohérente. Le grès se rencontre dans une grande variété de milieux de dépôt, comme les rivières ou les plages. Son équivalent non consolidé est traditionnellement appelé sable.
Variétés et caractéristiques : Le ciment et les éléments accessoires donnent à la roche sa couleur : la teinte jaune, orange, brun, rouge est fonction de la présence d'oxyde de fer. La teinte verdâtre tient à la présence de chlorite. La teinte noire à des oxydes de manganèse. La teinte grise provient de débris de roches sombres.
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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 :
1 - What process consolidates the grains of this rock ?
2 - Based on your observation, what is the color of this sandstone and what causes it ?
3 - Upon closer inspection, what color is it partially speckled with?
4 - Take a photo in this street, with your geocaching username visible, and make a 🤜 sign with your hand.
EarthCache 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 : Sandstone is a detrital sedimentary rock formed from the aggregation of grains and consolidated during diagenesis. The grains that constitute sandstone generally originate from the erosion of pre-existing rocks, which largely determine its composition, primarily quartz and feldspar. Depending on the degree of cementation and its composition, it can form a very friable or coherent rock. Sandstone is found in a wide variety of depositional environments, such as rivers and beaches. Its unconsolidated equivalent is traditionally called sand.
Varieties and characteristics : Cement and accessory elements give the rock its color: yellow, orange, brown, and red hues depend on the presence of iron oxide. A greenish tint is due to the presence of chlorite. A black tint is due to manganese oxides. A gray tint comes from debris of dark rocks.
Happy Géocaching everyone 😎