Glass‐rich chondrules in ordinary chondrites

Abstract There are two types of glass‐rich chondrules in unequilibrated ordinary chondrites (OC): (1) porphyritic chondrules containing 55–85 vol% glass or microcrystalline mesostasis and (2) nonporphyritic chondrules, containing 90–99 vol% glass. These two types are similar in mineralogy and bulk composition to previously described Al‐rich chondrules in OC. In addition to Si‐, Al‐ and Na‐rich glass or Ca‐Al‐rich microcrystalline mesostasis, glass‐rich chondrules contain dendritic and skeletal crystals of olivine, Al2O3‐rich low‐Ca pyroxene and fassaite. Some chondrules contain relict grains of forsterite ± Mg‐Al spinel. We suggest that glass‐rich chondrules were formed early in nebular history by melting fine‐grained precursor materials rich in refractory (Ca, Al, Ti) and moderately volatile (Na, K) components (possibly related to Ca‐Al‐rich inclusions) admixed with coarse relict forsterite and spinel grains derived from previously disrupted type‐I chondrules.