BH250-81
Title
BH250-81
Subject
Granite
Description
Major Minerals: perthite, antiperthite, albite, hornblende, quartz, fluorite
Minor Minerals: microcline, zircon, biotite, sphene (titanite), spinel, monazite, allanite
Mineralogy Comments: large zoned zircons; hornblende altered to chlorite; allanite mostly altered; euhedral monazite common
The rock exhibits a coarse-grained (phaneritic) texture, with euhedral to subhedral hornblende and perthitic to antiperthitie. Quartz occurs as anhedral grains, typically filling interstitial spaces between feldspars, characteristic of a graphic granite texture.
Accessory minerals, including zircon, sphene (titanite), apatite and monazite, are very common in this thin sections and you will find many photomicrographs in this page. Zircons are notably large and zoned, reflecting complex magmatic histories. Allanite is mostly altered, and well-formed euhedral monazite crystals are common.
Accessory minerals like zircon, apatite, monazite, and sphene (titanite) are highly valuable in geochronology because they naturally concentrate uranium (U), thorium (Th), and other trace elements essential for radiometric dating.
Resistant minerals such as zircon and monazite often preserve multiple growth zones, enabling in-situ dating using techniques like LA-ICP-MS and SIMS. These methods can generate detailed age-depth profiles within a single grain. Additionally, coupling geochronology with isotopic systems (e.g., Lu-Hf in zircon, Sm-Nd in monazite) provides insight into the source characteristics and crustal evolution.
Learning to identify these minerals and separate them from the bulk rock for dating is one of the most valuable skills in geochronology.
Minor Minerals: microcline, zircon, biotite, sphene (titanite), spinel, monazite, allanite
Mineralogy Comments: large zoned zircons; hornblende altered to chlorite; allanite mostly altered; euhedral monazite common
The rock exhibits a coarse-grained (phaneritic) texture, with euhedral to subhedral hornblende and perthitic to antiperthitie. Quartz occurs as anhedral grains, typically filling interstitial spaces between feldspars, characteristic of a graphic granite texture.
Accessory minerals, including zircon, sphene (titanite), apatite and monazite, are very common in this thin sections and you will find many photomicrographs in this page. Zircons are notably large and zoned, reflecting complex magmatic histories. Allanite is mostly altered, and well-formed euhedral monazite crystals are common.
Accessory minerals like zircon, apatite, monazite, and sphene (titanite) are highly valuable in geochronology because they naturally concentrate uranium (U), thorium (Th), and other trace elements essential for radiometric dating.
Resistant minerals such as zircon and monazite often preserve multiple growth zones, enabling in-situ dating using techniques like LA-ICP-MS and SIMS. These methods can generate detailed age-depth profiles within a single grain. Additionally, coupling geochronology with isotopic systems (e.g., Lu-Hf in zircon, Sm-Nd in monazite) provides insight into the source characteristics and crustal evolution.
Learning to identify these minerals and separate them from the bulk rock for dating is one of the most valuable skills in geochronology.
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-81. Housed at Carleton College in Minnesota.
Type
Thin section
Relation
Collection
Citation
Bereket Haileab, “BH250-81,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/91.