Hematite

A sample of hematite. Credit goes to the Brigham Young University Geology
Department and Andrew Silver, the photographer.

An important iron ore, hematite (Fe2O3) is a mineral that is mostly metal and comes in more than one form (one of which is specularite/specular hematite.) For the ancient Maya, this mineral was useful as a coloring for different things, including in burials.

A sample of specular hematite. Courtesy US 
Geological Survey/photo by Scott Horvath.

Processing It
The ancient Maya turned hematite into powder -- then to paint with it, they added powder. Turning hematite into powder was not easy. Because it wasn't easy to make, hematite powder wasn't cheap, so it was easier to get if you were an elite Maya.

Uses
Hematite was one of the things that the ancient Maya inserted into their teeth as a fashion statement. (Another mineral they inserted into their teeth was jade.)

The ancient Maya used it as one of several pigments for coloring people's bodies or the cloth used as their shroud after those people had passed on. (The other was cinnabar, which is less easily found than hematite -- it's more dangerous as well, because part of its makeup is mercury. Sometimes the Maya used both.) How this was specifically done depended somewhat on the site. Elites were the ones who did had their bodies colored red most often. This was because they were able to afford it.

Other than for bodies of the dead, the ancient Maya used hematite to color things. They used it as paint for ceramics, murals, and cloth. They also used it as a red body paint for living people -- a known example of body painting is images where elites are painted different colors. (On a related note, at Joya de Cerén, a site in El Salvador, it was found that all the houses had a container of hematite pigment -- some had more than one.)

Hematite was also a material that the ancient Maya would use to make mirrors. (Based on what's been found in burials, the Maya in the highlands made mirrors more than the ones in the lowlands.)

Meaning
There's a theory that the ancient Maya thought of hematite as having a symbolic meaning. They may have thought of it as being like blood.

References:
Google Books: "cosntructing Power & Place in Mesoamerica: Pre-Hispanic Paintings from Three Regions"; Merideth Paxton, Leticia Staines Cicero (editors); 2017

Google Books: "Mortuary Landscapes of the Classic Maya: Rituals of Body and Soul"; Andrew K. Scherer; 2015

Google Books: "The Ancient Maya Marketplace: The Archaeology of Transient Space"; Eleanor M. King (editor); 2015

Google Books: "Death and the Classic Maya Kings"; James L. Fitzsimmons; 2009

Google Books: "Field Guide to Rocks & minerals of Southern Africa"; Bruce Cairncross; 2004

Image Credits:
USGS: ScienceBase - Catalog: Hematite

USGS: Specularite; Scott Horvath