From the Soil Micromorphology Slide Collection

Micromorphological description of slide: Biogenic calcite in earthworm casts--illustrated in BF-32-here under high magnification. Calcite crystals are micro in size, euhedral to anhedral in form and show obtuse rhombohedral symmetry.

Data for the horizon
Horizon sampled: Ah 1
Depth sampled: 0-18 cm
Physical and chemical data available: pH = 7.2; OC = 5.0 0/01 N = 0.31 %; TEC (cmol (+)/kg) = 20; total clay 12%, fine clay = 7%; clay mineralogy = smectite > mica > kaolinite.
Macromorphological description of horizon: Ahi (0-18 cm): Black (10 YR 1 .7/1 m); sandy loam; weak to moderate fine granular; very friable; abundant fine and very fine random, plentiful medium oblique roots; clear wavy boundary; 12-20 cm thick.
Micromorphological description Of horizon: The Ah horizon has an iunctic granic/granoidic intergrade f-fabric with 8 weak chlamydic component. Dominantly fine (50-150 pm) discrete and partially coalesced organic and mull units loosely fill spaces between large f-members dominantly comprised of mineral grains and to a much lesser extent decomposed organic tissue. Mineral grains have partial coatings of organic and mull-like plasma. Numerous large (5 mm diameter) isotubules and aggrotubules filled with discrete (1 .0-1 .5 mm) and strongly welded earthworm casts occur near the surface. Earthworm casts contain small humigranic units, occasionally fecal pellets of micro arthropods, and rarely zones of biogenic micro crystals of calcite. Fecal pellets of small Diptera (fly) larvae (90-225 pm) occur as weakly welded clusters in voids; fecal pellets of mites (35-70 pm) commonly occur in decomposing plant tissue; and fecal pellets of Enchytraeids (potworms) (90-1 20 um) occur in aggrotubules. Aragonite crystal sheets are evident in decomposing plant tissue.

Data for thin section
Preparation of sample: Air dry
Impregnating medium: Epoxy
Thickness of section: 30 µm
Orientation of section: Vertical

Soil Classification
U.S.: Cryoboralf
F.A.O.: Chernozem Canada: Orthic Black Chernozemic

Elevation: 795 m
Topography and hill slope position: Rolling slope crest
Parent material: Glacial/fluvial
Soil climatic data and/or soil water balance: Subhumid moisture regime and cold soil temperature class
Vegetation: Trembling aspen (Populus tremuloides) parkland

Data for 35-mm slide
Frame length: 0.25 mm
Light mode: Cross-polarized

Source: S. Pawluk

Slide BF19. Soil Science Society of America, 1993. A Reference Slide Collection for Soil Micromorphology. SSSA, Madison, WI.