[8] Resentful of her beauty, she radically changed her image – dyeing her hair red and wearing black clothes in an effort to distance herself from what had made her a popular fashion model.

In the poem Wordsworth contemplates a statue of Isaac Newton in the chapel of Trinity College, Cambridge: "with his prism and silent face / The marble index of a mind for ever / Voyaging through strange seas of Thought, alone.

[16] The finished album was barely 30 minutes long, which "was as much apparently as Frazier Mohawk, mixing and sequencing it, could stand without starting to feel suicidal".

[8] With Nico's compositions based around one or two chords,[1] Cale decided to avoid drone and raga (Eastern music common on the West Coast at the time) in favor of a European classical approach in his arrangements.

[19] Peter Buckley noted Nico's use of psychedelic drugs during the Summer of Love as an influence on the album's music,[22] and Jim DeRogatis described it as "minimalist bad-trip psychedelia".

[25] Isolationism, Reynolds writes, "breaks with all of ambient's feel-good premises" and "evokes an uneasy silence: the uncanny calm before catastrophe, the deathly quiet of aftermath".

[25] He listed Aphex Twin (particularly his 1994 album Selected Ambient Works Volume II), Seefeel, David Toop and Max Eastley, among others, as exponents of this style.

[20][27][28] André Escarameia felt the album "anticipated gothic rock by more than a decade due to [its] ethereally darker [ambience] and disturbing sonority.

[32] Regarding the record's sonority, British author Simon Goddard wrote, "it was on [The Marble Index] that the real sound of Nico was unleashed: a bleak pumping misery which would define her music for the last two decades of her life.

"[12] Stephen Davis wrote that the album's lyrics stem from the collaboration between Nico and Morrison, and his influence can be seen in song titles such as "Lawn of Dawns", "Frozen Warnings" and "Evening of Light".

[37] For example, Richie Unterberger wrote: "Nico intones lyrics that don't quite express specific feelings but convey a state of uneasy restlessness.

[40] The album begins with a gentle piano-and-glockenspiel instrumental before segueing into "Lawn of Dawns", which introduces Nico's harmonium "of undulating motion weaving against her voice".

"[6] Nico explained the peyote-induced experience which inspired the lyrics: "The light of the dawn was a very deep green and I believed I was upside down and the sky was the desert which had become a garden and then the ocean.

"[6] The lyrics of the next song, "No One Is There", have been described as "in all probability influenced by Jim Morrison" ("Some are calling/Some are sad/Some are calling mad") and are sung over Cale's classical quartet of violas darting in and out of her unusual vocal tempo.

Nico sings "Midnight winds are landing at the end of time", with harpsichord and Cale's staccato viola building until the latter gains ground and sways with the tympani's "roar and clatter".

The full version (with instrumental accompaniment) was included in the 2007 compilation The Frozen Borderline – 1968–1970; according to Dave Thompson of AllMusic, "It rises to equal any of Nico's subsequent performances or compositions.

[8] A music video for "Evening of Light", featuring Iggy Pop and the other Stooges, was shot by the art collector François de Menil in 1969.

[44] The Marble Index "failed to challenge the supremacy of Nashville Skyline, From Elvis in Memphis, Abbey Road and Diana Ross & the Supremes Join the Temptations on the album charts of 1969".

[47] Although The Marble Index was generally unnoticed when it was released, it was praised by the countercultural East Village Other and International Times;[41] however, most critics found "her desolate soundscapes inaccessible.

"[22] Anne Marie Micklo of Rolling Stone gave the album a positive review, calling side two "a really worthwhile venture into musical infinity".

[37] Anthony Carew of About.com called it "a suite of rootless songs written with little precedent" and "an astonishing haunting, the work of a woman who, even whilst alive, seemed a lot like a ghost".

[9] Anthony Thornton of NME called it an "artistic triumph": "Bleak but beautiful, this album remains the most fitting embodiment of her doomed glamour.

[17] Dorian Lynskey wrote for The Guardian that The Marble Index forces the distinction between art and entertainment, comparing it to the "terrifying" output of musician Scott Walker (particularly the album Tilt), painter Mark Rothko and writer Philip Roth.

[30] Simon Reynolds described the record as "psychic landscapes, glittering in their immaculate, lifeless majesty of someone cut off from the thawing warmth of human contact and fellowship"[5] and "religious music for nihilists".

[13] Sputnikmusic's Louis Arp was less enthusiastic, finding the music "pretentious" and "agitating" in the aura it evoked while deeming Nico's lyrics repetitive and meaningless.

[27] According to Spin, "[The Marble Index] set the tone for decades of music to come – Arthur Russell, Dead Can Dance, Fennesz, Zola Jesus, Grouper, pretty much every metal band that ever used a harpsichord – but few followers have sailed so near to the edge of the abyss with such chillingly beautiful results.

"[13] In The Marble Index Nico took this persona (originally embodied by Grace Slick) even further, making a fetish of disconnection and "[dreaming] of a sort of negative nirvana".

[64] She lived in the United Kingdom when the gothic rock scene was developing, with supporting acts including the Sisters of Mercy and Gene Loves Jezebel.

"[2] The album's release coincided with a change in Nico's look, when she adopted what has been called a "gothic horror princess" persona[65] and "switched from dyed blonde to dark henna and started wearing black, heavy fabrics and boots".

[38] Claire Marie Healy wrote, "Nico's visual statement of these years speaks of the power that comes with creating a new persona for yourself"[20] and she described the singer as "the first ever goth girl".