Shares in commodities trading group Glencore fell below their issue price of 530 pence on Friday, the second day of conditional trading, as investors fretted over its valuation.

The world's largest diversified commodities trader touched a low of 519 pence in unofficial grey market trade before closing at 524 pence, down 1.1 percent after more than 200 million shares changed hands, underperfoming a virtually flat FTSE index and a 0.4 percent dip in the broad mining sector.

The shares had closed on Thursday at 530 pence, exactly flat on a debut price in the middle of its indicated range, after a day of heavy volumes -- more than twice Friday's levels -- that made it one of the most traded stocks in the market.

Basically, the valuation looks a little bit rich. They worked very hard to get a favorable price and one could argue the only reason it was up yesterday was support from the sponsoring banks, said analyst Nik Stanojevic at Brewin Dolphin.

I think the market feels the same way. It wasn't as if they sold this thing really cheaply with the expectation it would go up 50 percent on the first day.

Unconditional trading begins on Tuesday in London, where Glencore's offer of up to $11 billion is set to be the largest listing on record, and Wednesday in Hong Kong.

Glencore, the world's largest diversified commodities trader, has said there was strong demand for its stock and it had enough buyers to cover its offering of up to $11 billion within hours of starting the sale process earlier this month.

But many investors have also expressed concern over the outlook for commodities, particularly after this month's sell-off, and fretted over the discounts that should be applied to take account of Glencore's conglomerate structure and of the fact it has operated away from the public eye for 37 years.

Perhaps the fact that the float has, despite being over four times covered, been met with broad skepticism and sobriety is a sign of underlying health in the metals market? analysts at Numis said in a morning note.

The hopes for a 5-10 percent rally remain -- not exactly LinkedIn, but the first objective remains stability and garnering faith in this new currency.

Professional social networking site LinkedIn saw its shares more than double in their public trading debut on Thursday, a far cry from Glencore's more muted start.

At the offer price of 530 pence, Glencore has a market value of 36.7 billion pounds ($59.3 billion). It will be the fifth-largest mining-related company on the London exchange.

(Reporting by Clara Ferreira-Marques; Editing by Alexander Smith and Will Waterman)