Question: What genre of music was the album The Sabbath Stones?
Context: This is an incomplete list of heavy metal festivals.  Heavy metal (or simply metal) is a genre of rock music that developed in the late 1960s and early 1970s, largely in the United States and the United Kingdom.  With roots in blues rock and psychedelic rock, the first heavy metal bands such as Led Zeppelin, Black Sabbath and Deep Purple attracted large audiences, and during the late 1960s and mid-1970s these band and others in their genre were featured at a number of historic rock festivals. Judas Priest helped spur the genre's evolution by discarding much of its blues influence. Doom metal is an extreme style of heavy metal music that typically uses slower tempos, low-tuned guitars and a much "thicker" or "heavier" sound than other metal genres.  Both the music and the lyrics intend to evoke a sense of despair, dread, and impending doom.  The genre is strongly influenced by the early work of Black Sabbath, who formed a prototype for doom metal with songs such as "Black Sabbath", "Children of the Grave", "Electric Funeral" and "Into the Void".  During the first half of the 1980s, a number of bands from England (Pagan Altar, Witchfinder General), the United States (Pentagram, Saint Vitus, Trouble) and Sweden (Candlemass, Count Raven) defined doom metal as a distinct genre. Nativity in Black is the name of two Black Sabbath tribute albums that came out in the 1990s and 2000s.  The albums were recorded with various heavy metal bands paying tribute to Black Sabbath for their influence on the heavy metal genre of rock music. Masters of Reality was a Heavy Post Progressive Rock Band formed in 1981-1986 by vocals frontman Chris Goss, lead guitar Tim Harrington, lead keyboards Mr. Owl, Keyboard Googe from Syracuse, New York.  A band that was a combination early King Crimson and early Black Sabbath, with original songs, like: Building the Kingdom, Voodoo Doll, Metal Entity, M.O.R., Cash, Anchor, Stones in Every Field, Doraldina's Prophecies, just to name a few The band is sometimes associated with the "Palm Desert Scene", after the first lineup which includes bands like Kyuss, Queens of the Stone Age and many other stoner rock or (as they prefer to call it) "desert rock" bands.  The band is named after the album "Master of Reality" by Black Sabbath. Black Sabbath were an English rock band, formed in Birmingham in 1968, by guitarist and main songwriter Tony Iommi, bassist and main lyricist Geezer Butler, singer Ozzy Osbourne, and drummer Bill Ward.  Black Sabbath are often cited as pioneers of heavy metal music.  The band helped define the genre with releases such as "Black Sabbath" (1970), "Paranoid" (1970) and "Master of Reality" (1971).  The band had multiple line-up changes, with Iommi being the only constant member throughout its history. "Hand of Doom" is a song by the English heavy metal band Black Sabbath, originally appearing as the sixth song on their second album "Paranoid", released in 1970.  It has been performed in many of Black Sabbath's live concerts.  The lyrics were written by Geezer Butler while the music was written by the four members.  "Hand of Doom" is accepted as one of the best songs on the album by many fans of Black Sabbath.  It is the second longest song on the album behind "War Pigs". The Sabbath Stones (1996) is a compilation album of Black Sabbath songs taken from albums ranging from 1983's "Born Again" to 1995's "Forbidden".  It was never formally released in the US or Canada, and was the last album to be released by Black Sabbath with I.R.S. Records. "Heaven and Hell" is the title track to Black Sabbath's ninth studio album of the same name.  The music was written mainly by Tony Iommi, but as with almost all Black Sabbath albums, credit is given to the entire band.  The lyrics were written entirely by then newcomer Ronnie James Dio.  The song has been performed by several bands of which Iommi and Dio were members including Black Sabbath, Dio, and Heaven & Hell. Black Sabbath is the debut album by the English rock band Black Sabbath.  Released on 13 February 1970 in the United Kingdom and on 1 June 1970 in the United States, the album reached number eight on the UK Albums Charts and number 23 on the "Billboard" charts.  Although it was poorly received by most contemporary music critics at the time, "Black Sabbath" is now widely considered the first heavy metal album. Witchcraft Destroys Minds & Reaps Souls is the debut studio album by the American psychedelic rock band Coven.  Released in 1969, it was unusual in that it dealt with overtly occult and satanic themes, and was removed, in the past time, from the market soon after its release due to controversy.  However, it remains a classic of its genre, and in some ways set groundbreaking trends for later rock bands.  This album marked the first appearance in music of the sign of the horns, inverted crosses, and the phrase Hail Satan.  Today, these are characteristics of the occult and heavy metal genres.  According to rock journalist Lester Bangs, "in England lie unskilled laborers like Black Sabbath, which was hyped as a rockin' ritual celebration of the Satanic mass, something like England's answer to Coven".  As a further coincidence, Coven's bass guitarist and co-writer (Mike Osborne) is credited as "Oz Osborne", and the opening track is "Black Sabbath".
Answer: heavy metal music