{"id":52,"date":"2026-01-15T19:01:11","date_gmt":"2026-01-15T19:01:11","guid":{"rendered":"https:\/\/www.geol.umd.edu\/facilities\/probe\/?page_id=52"},"modified":"2026-01-15T19:02:16","modified_gmt":"2026-01-15T19:02:16","slug":"how-do-you-calculate-the-weight-of-elements-from-a-mineral-molecular-formula","status":"publish","type":"page","link":"https:\/\/www.geol.umd.edu\/facilities\/probe\/how-do-you-calculate-the-weight-of-elements-from-a-mineral-molecular-formula\/","title":{"rendered":"How do you calculate the weight % of elements from a mineral (molecular) formula?"},"content":{"rendered":"
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\n\t

How do you calculate the weight % of elements from a mineral (molecular) formula?<\/h1>\n

To do so, you will first need to determine the molecular weight of the mineral.<\/p>\n

For example: KAlSi3<\/sub>O8<\/sub><\/p>\n

    \n
  1. Set up a table with 5 columns, placing the element name in the first column.<\/li>\n
  2. In column 2, enter the number of atoms of the element in the mineral formula.<\/li>\n
  3. In column 3, enter the atomic weight of each of the elements in the mineral (if you don't know these, consult a periodic table).<\/li>\n
  4. Multiply the value in column 2, by the atomic weight in column 3, and enter the results in column 4 (in the case of O, 8 x 15.999 = 127.992).<\/li>\n
  5. Sum the values in the column 4 (and enter the sum at the bottom; e.g. 278.330)<\/li>\n
  6. To calculate the weight % of the element in the mineral, divide the value for the contribution to the molecular weight (for example, O 127.992), divided by the sum of the contributions (278.330), and multiply by 100 (to arrive at 45.99 weight % for O)<\/li>\n<\/ol>\n\n\n\n\n\n\n\n\n
    Element<\/th>\nNumber of Atoms in Formula<\/th>\nAtomic Weight<\/th>\nContribution to Molecular Weight<\/th>\nWeight % Element in Mineral<\/th>\n<\/tr>\n
    K<\/td>\n1<\/td>\n39.098<\/td>\n39.098<\/td>\n14.05<\/strong><\/td>\n<\/tr>\n
    Al<\/td>\n1<\/td>\n26.982<\/td>\n26.982<\/td>\n9.69<\/strong><\/td>\n<\/tr>\n
    Si<\/td>\n3<\/td>\n28.086<\/td>\n84.258<\/td>\n30.27<\/strong><\/td>\n<\/tr>\n
    O<\/td>\n8<\/td>\n15.999<\/td>\n127.992<\/td>\n45.99<\/strong><\/td>\n<\/tr>\n
    <\/td>\n<\/td>\n<\/td>\n278.330<\/td>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div><\/div><\/div><\/div><\/div>","protected":false},"excerpt":{"rendered":"

    How do you calculate the weight % of elements from a mineral (molecular) formula? To do so, you will first […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"default","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"set","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"class_list":["post-52","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.geol.umd.edu\/facilities\/probe\/wp-json\/wp\/v2\/pages\/52","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.geol.umd.edu\/facilities\/probe\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.geol.umd.edu\/facilities\/probe\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.geol.umd.edu\/facilities\/probe\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.geol.umd.edu\/facilities\/probe\/wp-json\/wp\/v2\/comments?post=52"}],"version-history":[{"count":2,"href":"https:\/\/www.geol.umd.edu\/facilities\/probe\/wp-json\/wp\/v2\/pages\/52\/revisions"}],"predecessor-version":[{"id":54,"href":"https:\/\/www.geol.umd.edu\/facilities\/probe\/wp-json\/wp\/v2\/pages\/52\/revisions\/54"}],"wp:attachment":[{"href":"https:\/\/www.geol.umd.edu\/facilities\/probe\/wp-json\/wp\/v2\/media?parent=52"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}