{"id":2252,"date":"2026-08-12T11:47:37","date_gmt":"2026-08-12T09:47:37","guid":{"rendered":"https:\/\/mineralien-weltweit.com\/product\/calcite-iceland-spar-mahajanga-madagascar\/"},"modified":"2026-08-17T16:38:30","modified_gmt":"2026-08-17T14:38:30","slug":"calcite-iceland-spar-mahajanga-madagascar","status":"publish","type":"product","link":"https:\/\/mineralien-weltweit.com\/en\/product\/calcite-iceland-spar-mahajanga-madagascar\/","title":{"rendered":"Calcite Iceland Spar from Mahajanga, Madagascar \u2013 Distinct Birefringence"},"content":{"rendered":"<p class=\"isSelectedEnd\">This transparent to translucent calcite Iceland spar specimen from Mahajanga Province, Madagascar displays one of calcite\u2019s most characteristic optical properties particularly well: pronounced birefringence (Double refraction).<\/p>\n<p class=\"isSelectedEnd\">Through the clearer areas of the specimen, underlying lines or lettering appear distinctly doubled. This optical effect is caused by the strong birefringence of calcite and can be observed directly in this specimen. <\/p>\n<h3>Transparent calcite with visible birefringence (Double refraction)<\/h3>\n<p class=\"isSelectedEnd\">The specimen has a flat, rhombohedral appearance and shows good transparency over larger areas. Natural cleavage surfaces, slight cloudiness and internal structural irregularities are visible within the calcite. Some areas also produce subtle colored light reflections.  <\/p>\n<p class=\"isSelectedEnd\">The double refraction can be observed especially well when the specimen is placed over writing, lines or other high-contrast patterns. This makes the calcite not only an interesting collector specimen, but also a particularly illustrative example of the optical properties of this mineral. <\/p>\n<h3>Iceland spar from Madagascar<\/h3>\n<p class=\"isSelectedEnd\">Madagascar is known for a wide variety of mineral localities. Transparent calcite of optical quality is also documented from Mahajanga Province. In this specimen, the main appeal lies less in an unusual crystal habit and more in the clarity, pronounced cleavage and clearly visible birefringence.  <\/p>\n<p class=\"isSelectedEnd\">With dimensions of 6.0 \u00d7 5.0 \u00d7 1.8 cm and a weight of 121.3 g, this is a substantial Small cabinet specimen whose optical effect can already be demonstrated clearly with the naked eye.<\/p>\n<table>\n<tbody>\n<tr>\n<th>Feature<\/th>\n<th>Details<\/th>\n<\/tr>\n<tr>\n<td>Mineral<\/td>\n<td>Calcite<\/td>\n<\/tr>\n<tr>\n<td>Variety\/ Trade name<\/td>\n<td>Iceland spar \/ optical calcite<\/td>\n<\/tr>\n<tr>\n<td>Locality<\/td>\n<td>Mahajanga Province, Madagascar<\/td>\n<\/tr>\n<tr>\n<td>Dimensions<\/td>\n<td>6.0 \u00d7 5.0 \u00d7 1.8 cm<\/td>\n<\/tr>\n<tr>\n<td>Weight<\/td>\n<td>121.3 g<\/td>\n<\/tr>\n<tr>\n<td>Size category<\/td>\n<td>Small cabinet specimen<\/td>\n<\/tr>\n<tr>\n<td>Color<\/td>\n<td>Colorless to slightly whitish<\/td>\n<\/tr>\n<tr>\n<td>Transparency<\/td>\n<td>Transparent to translucent<\/td>\n<\/tr>\n<tr>\n<td>Luster<\/td>\n<td>Vitreous luster on smooth surfaces<\/td>\n<\/tr>\n<tr>\n<td>Crystal habit<\/td>\n<td>Rhombohedral<\/td>\n<\/tr>\n<tr>\n<td>Special Feature<\/td>\n<td>\nClearly visible birefringence (Double refraction)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n","protected":false},"excerpt":{"rendered":"<p>This transparent to translucent calcite Iceland spar specimen from Mahajanga Province, Madagascar displays one of calcite\u2019s most characteristic optical properties particularly well: pronounced birefringence (Double refraction). Through the clearer areas of the specimen, underlying lines or lettering appear distinctly doubled. This optical effect is caused by the strong birefringence of calcite and can be observed [&#8230;]\n","protected":false},"featured_media":2249,"comment_status":"open","ping_status":"closed","template":"","meta":[],"product_brand":[],"product_cat":[455,351],"product_tag":[],"class_list":["post-2252","product","type-product","status-publish","has-post-thumbnail","product_cat-calcite","product_cat-minerals","first","instock","sold-individually","shipping-taxable","purchasable","product-type-simple"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.5 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Calcite Iceland Spar from Madagascar | Visible Birefringence<\/title>\n<meta name=\"description\" content=\"Transparent calcite Iceland spar from Mahajanga, Madagascar, with clearly visible birefringence (Double refraction). 6 cm Small cabinet specimen weighing 121.3 g.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, 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