"Heat, pressure, and time," Wolfe said regarding the formation of anthracite. "These men were the foundation, and there was this geological foundation - a sense of it all being buried deep into the earth.
"The first movement . . . opens with this low rumble. Little by little, you hear the names [of miners], names that I recognize. I know somebody with those names somewhere in my life. It became very personal."
The Montgomeryville native receives commissions from modern-music organizations all over the world, but Anthracite Fields is her first from Philadelphia, and she wanted to touch on something local. "Something about tunnels and digging was speaking to me," she said.
Soon the composition's subject turned into a bottomless pit. Anthracite Fields will be performed in the candlelit Philadelphia Episcopal Cathedral with singers costumed in tunics printed with Photoshopped coal - "as if you're looking at the wall in a mine," says designer Katy Coble.
Choreographer Leah Stein is adding movement. At times, the singers will bend to the side, as though peering deep into the ground - "but in a subtle way," Stein says. "I'm not trying to make it theatrical, but to do something that will expand the audience's experience."
The piece itself is full of pictorial imagery - the above-ground flowers that were meticulously tended to bring color into miners' black-and-gray lives, a refined female character used to advertise the cleanness of trains fueled by coal.
Elsewhere, Wolfe sets speeches by labor activist John L. Lewis to music.
"Lewis was a god in my house," said longtime Mendelssohn Club director Alan Harler, son of a coal miner in Galesburg, Ill. He saw the effects of black-lung disease and lived through long strikes during which his father hunted quail not for sport but for dinner.
But when accompanying Wolfe on a coal mine visit, Harler got no farther than the entrance. "Claustrophobia," he says. "Just the thought of it . . . and I could hardly breathe."
Wolfe often asked herself what she was getting into when she first drove out to the Scranton area for research. "I thought, 'Why am I looking at this?' It's a very loaded subject - political issues, environmental issues, immigrant issues, people who persevered, made a life and fueled the nation. Who are these people?"
Touring the No. 9 Coal Mine in Lansford with Wolfe, one understands why she was so taken in by this world. The well-kept town seems to exist in a 1950s time warp. The mine itself, which operated from 1855 to 1972, was dripping with water from still-melting snow.
In this underground environment, a homey-looking storefront was a first-aid station. Mules lived here. Steam engines wheezed. Deaths were frequent and bizarre. One man who physically abused a mule was the object of the animal's revenge: It crushed him against a wall. Another man was trapped by an engine and cooked to death.
Tour guide Dave Kutcha - who has heard the "don't leave me" ghost - talked about how his 36-year-old grandfather was asphyxiated when a steam engine in a tunnel below him broke down.
Yet not all was bleak. Many took pride in what they felt was the most honest of work: "Everybody hung out together. Everybody helped each other. If somebody was sick that day, the others covered for him. It was an extended family," says Wolfe. "They lived in these impoverished houses but never felt poor."
Even kids too young to work in the mines had the grueling task of picking shale from the coal (without gloves and, later, without fingernails). But they still had fun with games reflected in the nursery-rhyme lyrics Wolfe uses in the "Breaker Boys" movement of the piece.
Tour guide Kutcha was not one of them. "My father told me in no uncertain terms - you'd better not even think of working in a mine here," he said. "So I got a job at Bethlehem Steel. But I've lived in this region all my life. Coal is in my blood."
In such company, Wolfe's musical vocabulary changed. Known for melodically severe, rhythmically propulsive works for massed bagpipes or double basses, she revealed something richer in Steel Hammer (2009), a 90-minute work about the mythical railroad worker John Henry. A Pulitzer Prize finalist, the piece comes out this spring on CD. But rehearsals for Anthracite Fields reveal a further blossoming into richer harmonies, expansive vocal lines, and sound effects Harler still ponders.
One movement ends with haunting D-minor whistling. "What is that?" he asks. "A canary?"
Though Wolfe considers the piece's current state complete - it will also be performed as part of the New York Philharmonic's Biennial in late May - she's not finished. She longs to add movements inspired by John Mitchell, the labor leader who united rival ethnic groups by saying the coal was not Irish or Polish or Welsh: "It's coal."
And then? The rats, which knew when cave-ins were about to happen and unintentionally led many miners to safety. "I'd really like to do a rat movement. I just didn't get to it," she says. "The [miner] boys were friendly with the rats. They'd save crusts of bread for them."
At 4 and 7:30 p.m. Saturday and next Sunday at the Philadelphia Episcopal Cathedral, 13 S. 38th St.
Tickets $28-30. Information: 215-735-9922 or www.mcchorus.org.