{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,15]],"date-time":"2026-02-15T15:21:16Z","timestamp":1771168876097,"version":"3.50.1"},"reference-count":57,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2018,4,2]],"date-time":"2018-04-02T00:00:00Z","timestamp":1522627200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Minerals"],"abstract":"<jats:p>During a study aiming to recover strategic elements and minerals from coal fly ash and bottom ash (RAREASH and CHARPHITE projects funded, respectively, by the 2nd ERA-MIN and 3rd ERA-MIN Programs of the European Union Commission), it was found that in coal fly ash and bottom ash from Romania and Poland, several morphotypes did not fit into the general fly ash classifications, unless grouped together as \u201cundifferentiated inorganics\u201d. However, the combination of reflected light optical microscopy under oil immersion, scanning electron microscopy, and X-ray microanalysis (SEM\/EDS) showed that many of these morphotypes not only have distinctive petrographic patterns but are also characterized by a chemical assemblage dominated by Ca, Mg, and P. In this paper, a survey of the literature is presented together with several detailed studies of samples from the RAREASH and CHARPHITE projects from which the following nomenclature are proposed: \u201ccalcispheres\u201d for spongy Ca-rich morphotypes, \u201ccalcimagnesiaspheres\u201d for (Ca + Mg)-rich morphotypes with visible MgO nodules and\/or periclase (MgO) exsolved from Ca aluminate-silicate glass, and \u201cmagnesiaspheres\u201d divided into \u201cmagnesiaferrospheres\u201d for (Mg + Fe)-rich morphotypes with magnesioferrite, and \u201cmagnesiaoxyspheres\u201d for magnesiaspheres mainly composed of (Mg + Fe)-rich amorphous material with visible MgO nodules and\/or periclase.<\/jats:p>","DOI":"10.3390\/min8040140","type":"journal-article","created":{"date-parts":[[2018,4,2]],"date-time":"2018-04-02T12:32:20Z","timestamp":1522672340000},"page":"140","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":27,"title":["Undifferentiated Inorganics in Coal Fly Ash and Bottom Ash: Calcispheres, Magnesiacalcispheres, and Magnesiaspheres"],"prefix":"10.3390","volume":"8","author":[{"given":"Bruno","family":"Valentim","sequence":"first","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra (ICT), P\u00f3lo do Porto, Faculdade de Ci\u00eancias da Universidade do Porto (FCUP), Rua do Campo Alegre, 4169-007 Porto, Portugal"}]},{"given":"Barbara","family":"Bia\u0142ecka","sequence":"additional","affiliation":[{"name":"G\u0142\u00f3wny Instytut G\u00f3rnictwa, Central Mining Institute (GIG), plac Gwark\u00f3w 1, 40-166 Katowice, Poland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4841-8601","authenticated-orcid":false,"given":"Paula","family":"Gon\u00e7alves","sequence":"additional","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra (ICT), P\u00f3lo do Porto, Faculdade de Ci\u00eancias da Universidade do Porto (FCUP), Rua do Campo Alegre, 4169-007 Porto, Portugal"}]},{"given":"Alexandra","family":"Guedes","sequence":"additional","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra (ICT), P\u00f3lo do Porto, Faculdade de Ci\u00eancias da Universidade do Porto (FCUP), Rua do Campo Alegre, 4169-007 Porto, Portugal"}]},{"given":"Renato","family":"Guimar\u00e3es","sequence":"additional","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra (ICT), P\u00f3lo do Porto, Faculdade de Ci\u00eancias da Universidade do Porto (FCUP), Rua do Campo Alegre, 4169-007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9006-052X","authenticated-orcid":false,"given":"Mihai","family":"Cruceru","sequence":"additional","affiliation":[{"name":"Department of Automation, Energy, Environment and Sustainable Development, Faculty of Engineering, \u201cConstantin Br\u00e2ncu\u015fi\u201d University of T\u00e2rgu-Jiu, Eroilor 30, 210152 T\u00e2rgu Jiu, Romania"}]},{"given":"Joanna","family":"Ca\u0142us-Moszko","sequence":"additional","affiliation":[{"name":"G\u0142\u00f3wny Instytut G\u00f3rnictwa, Central Mining Institute (GIG), plac Gwark\u00f3w 1, 40-166 Katowice, Poland"}]},{"given":"Lumini\u0163a","family":"Popescu","sequence":"additional","affiliation":[{"name":"Department of Automation, Energy, Environment and Sustainable Development, Faculty of Engineering, \u201cConstantin Br\u00e2ncu\u015fi\u201d University of T\u00e2rgu-Jiu, Eroilor 30, 210152 T\u00e2rgu Jiu, Romania"}]},{"given":"Georgeta","family":"Predeanu","sequence":"additional","affiliation":[{"name":"University Politehnica of Bucharest, Research Center for Environmental Protection and Eco-Friendly Technologies (CPMTE), Polizu 1, Sector 1, 011061 Bucharest, Romania"}]},{"given":"Ana","family":"Santos","sequence":"additional","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra (ICT), P\u00f3lo do Porto, Faculdade de Ci\u00eancias da Universidade do Porto (FCUP), Rua do Campo Alegre, 4169-007 Porto, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2018,4,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1241","DOI":"10.1016\/S0016-2361(97)00065-3","article-title":"Unbiased methods for the morphological description of char structures","volume":"76","author":"Alvarez","year":"1997","journal-title":"Fuel"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1319","DOI":"10.1021\/ef010146z","article-title":"An approach toward a 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