Porphyritic granite gravestone (Hanover Cemetery, Hanover, Ohio, USA) 1 : 無料・フリー素材/写真
Porphyritic granite gravestone (Hanover Cemetery, Hanover, Ohio, USA) 1 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Gravestones (a.k.a. headstones / tombstones) in modern American cemeteries are usually made of "granite" - a term in the retail trade for any hard stone that will take a fine polish. Geologically, some are granites and some are not. In the 1800s, many gravestones were made of marble, a crystalline-textured metamorphic rock composed of calcite (calcium carbonate, CaCO3). Rainwater is naturally acidic (slightly), with carbonic acid - H2CO3. Over time, marble will slowly dissolve in rainwater. Older marble gravestones typically have poorly legible carvings.The gravestone seen here is made of porphyritic granite, a felsic, porphyritic, intrusive igneous rock. "Porphyritic" means a mix of large and small crystals. The pinkish-colored potassium feldspar crystals in this example are the large ones, called "phenocrysts". The smaller crystals are called "groundmass". Minerals in a typical granite include quartz, potassium feldspar, sodic plagioclase feldspar, amphibole, and mica. |
| 撮影日 | 2024-08-31 14:57:31 |
| 撮影者 | James St. John |
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