https://bereket-haileab.geology.sites.carleton.edu/files/original/ff133e8887d54103dfde9e30a5d365e2.jpg d89db339222e7e3f9d47e7befb7a7e34 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-173c Subject The topic of the resource Amygdaloidal Basalt Description An account of the resource Major Minerals: orthopyroxene, clinopyroxene, plagioclase Minor (secondary) minerals (vesicle fills): epidote, zeolite (notably exhibiting distinctive fan-shaped to radial crystal habits), chlorite (pennite variety), quartz Textyre: amygdaloidal basalt: Optics: Chlorite (pennite) displays characteristic berlin blue interference colors under cross-polarized light. Zeolites often appear as radiating or fan-shaped aggregates within vesicles, showing low birefringence and subtle extinction zoning. Amygdules and amygdaloidal basalt Vesicles in basalt filled with concentrically zoned secondary minerals are a striking result of post-eruption processes, recording interactions between fluids and solidified rock. Vesicles form when volatiles (e.g., H₂O, CO₂, SO₂) escape from magma during eruption. As lava cools rapidly, gas bubbles become trapped, leaving spherical or elongated cavities. After solidification, hydrothermal fluids or groundwater enter the basalt and deposit minerals inside the vesicles — a process known as amygdaloid formation. The infilled vesicles, called amygdules, contain secondary minerals. Amygdules are rounded, almond-shaped mineral deposits. These minerals often form concentric bands due to stepwise precipitation as fluid conditions change (e.g., temperature, pH, or chemistry). Early minerals coat the walls; later ones fill the center. Supersaturation of minerals like calcite or zeolites leads to layered deposition. Typical textures include: • Concentric banding – Alternating mineral layers • Botryoidal texture – Grape-like mineral masses • Zonation – Color or compositional variation from rim to core These features not only stand out visually but also reflect the history of fluid-rock interaction and may indicate low-grade metamorphism or hydrothermal alteration. Common secondary minerals include zeolites (see Mara MacDonell '17 comps), analcime, calcite, chlorite, and quartz, each marking shifts in post-volcanic conditions. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-173c. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=4639fbcb54694280bf3301cdd7e31651" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=4639fbcb54694280bf3301cdd7e31651">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RkYXrMk5dO4bpTpMGL3m4x0dRxfdJrzG/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1uTbqjoUymVU8PlzoCAsDKllY8TQFDHod/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1zmebAQNTa-jgShaNNt0Kvu6CikoIWcCE/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OoFh1p9ebjZhGU1YgjWKmMjHFbosLXqQ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1VpAr0Vv_UvKwVWmJLmQExiNEbUeIIQ6y/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fYJorVkDTUwro31LR-pTetLaX_Zu-0Rj/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hc2L8VCOx140iB4O-uj2Y0UHu1yExCq9/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ARnEF6NpcAePyOwOVpMb9R7oQBvu5et3/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Amygdaloidal basalt Amygdaloidal texture Amygdules basalt Berlin blue interference colors Botryoidal texture Chlorite (pennite) Clinopyroxene Concentric banding Concentric zoning Epidote Extinction zoning Fan-shaped zeolite Fluid-rock interaction Groundwater-rock interaction Hydrothermal alteration igneous Low birefringence Low-grade metamorphism Low-temperature mineralization mafic mafic volcanic rock Orthopyroxene Plagioclase Post-volcanic processes Quartz Radial zeolite Radiating aggregates Secondary minerals Spherical cavities Vesicle fills Vesicle formation Vesicle infill Vesicles vesicular basalt volcanic Volcanic rock Zeolite Zeolite facies alteration