Exhibit 4.2

                            SUPPLEMENTAL INDENTURE

     Reference is made to that certain Indenture, dated as of February 1, 1999,
by and among Oglebay Norton Company (formerly known as Oglebay Norton Holding
Company), a Delaware corporation ("Oglebay"), the guarantors party thereto and
NORWEST BANK MINNESOTA, NATIONAL ASSOCIATION, as Trustee (the "Indenture").
Capitalized terms used without definition herein have the meanings given to them
in the Indenture.

          RECITALS:

     A.  Section 4.13 of the Indenture provides, inter alia., that "[i]f (a) the
Company or any Restricted Subsidiary shall organize, acquire or otherwise invest
in another Person that becomes a Restricted Subsidiary, or (b) any Restricted
Subsidiary that is not already a Guarantor shall become an obligor under the
Senior Credit Facility, then the Company shall cause such Restricted Subsidiary
to (i) execute and deliver to the Trustee a supplemental Indenture pursuant to
which such Restricted Subsidiary shall become a Guarantor..."

     B.  A Restricted Subsidiary has organized MLO Properties, LLC, a Delaware
limited liability company, and MLO Properties, LLC is a Restricted Subsidiary
and is therefore required to become a Guarantor under the Indenture unless it is
designated as an Unrestricted Subsidiary;

     NOW, THEREFORE, in consideration of the above premises, MLO Properties, LLC
agrees, for the benefit of the Holders, as follows:

     Effective with the date hereof, MLO Properties, LLC hereby expressly and
fully and unconditionally agrees to become a Guarantor under the Financing
Documents.

     The laws of the State of New York shall govern this Supplemental Indenture
without giving effect to any conflicts of law principles thereof.

     IN WITNESS WHEREOF, the undersigned has caused this Supplemental Indenture
to be duly executed, as of April 26, 2000.

     MLO PROPERTIES, LLC                 NORWEST BANK MINNESOTA,
                                         NATIONAL ASSOCIATION

     By: /s/ Rochelle F. Walk            By:
        ---------------------                --------------------
          Rochelle F. Walk               Title:
          Assistant Secretary                  ------------------